warm-up · day 2

Remix: a classic your way

Today we'll give yesterday's game a different hero, setting and rule. First, we'll take a look at what makes the game work. We'll also write some notes for the agent, so you don't have to repeat the same instructions in every chat.

⏱ your time 60 min🎰 remix reelsyou need: the cartridge from Getting ready and its version history

by the end of the day your game gets

remix.html: your game with a different hero, setting, goal and rule
agent notes that carry over to a new chat

To compare: ask the agent to open remix.html, then index.html.

If you started with your own idea, keep working on it. Today, make a second version in remix.html and try one new rule. You don’t have to change the character or setting. Ask the agent to adapt the example prompts to your game.

Already used to breaking games down into rules? You can skip step 2. If your agent notes are ready too, head to the remix reels.

Play yesterday's version

Open the agent in your first-game folder (in the terminal: cd ~/games/first-game && claude) (in the terminal: cd ~/games/first-game && codex). Ask it to run the game, then play a round. Keep that version in mind as you work today.

Run the game.

Pick the game you made yesterday. The prompts and remix reels will use that choice.

Yesterday's version: the familiar hero, obstacles and score.

Today's version might be a snail in a spacesuit, jumping over asteroids and collecting 10 stars in moon gravity.

Played a round of yesterday's game

A quick recap

You saved your first change. The second broke the game before you saved it. What will restoring bring back?

The original game, without either changeYour last save already includes change 1. That change stays.
The game with change 1, without change 2Right. The files go back to your last save.
Both changes, with the bug removedRestoring brings back the saved version. It doesn't pick the good parts out of later changes.

You added a new background and increased the speed. Now the game stutters. Why is the cause hard to find?

The agent can't do two things at onceIt can. But you tested two changes together, so you don't know which caused the problem.
You don't know which change caused itYes. Changing and checking one thing at a time makes the cause easier to find.
Both changes used up the agent's limitThe limit isn't the issue. You tested both changes at the same time.

What a game is made of

We'll start with five parts of this runner:

Goalwhat the player is after

Actionwhat they press

Obstaclewhat gets in the way

Feedbackhow the game responds

Endwhen the round is over

You can switch off individual parts of this runner. Remove the goal and play for 10 seconds. Bring it back, then remove the end of the round. Watch the boredom meter on the right. What changes when those parts are missing?

take the game apartSwitch off a piece and play for 10 seconds

The boredom meter rises when pieces are missing, fastest with no goal. With all pieces in place, it drops. Also try “duck” against cacti.

Without a goal or a way to lose, you can still play around, but this runner gives you little to work toward. It's like kicking a ball: fun on its own, while goals and a score give you something to compete over.

The look isn't one of the five pieces, but it matters too. Luca Galante first built a Vampire Survivors prototype that played “exactly like Magic Survival”, and dropped it. Then he swapped the placeholder art for a bought pack of vampires and ghouls and “absolutely fell in love with the visuals”. Same rules, and the project came alive (PC Gamer, 2022).

You removed losing, so collisions no longer do anything. What changed in this runner?

It's a toy now: you run without taking a riskYes. Collisions gave this runner its risk. Without them, much of the tension disappears.
It got easier; everything else stayed the sameThe goal is still there, but dodging obstacles no longer matters. That changes how you play.
Nothing much: losing was a minor detailHere, the chance of losing gave you a reason to watch the obstacles.

Agent notes

Yesterday, we kept asking for the same things: one change at a time, numbers in CONFIG, and a way to check the result. Let's put those rules in a file the agent can read.

Agent notes live alongside the game. Claude Code uses CLAUDE.md.Codex uses AGENTS.md. Keep the rules you need for every change in that file.

Create a file CLAUDE.mdAGENTS.md in this folder: notes for you. You read it at the start of every chat. Write down 6 rules: 1. Answer in plain, simple English. A technical term only with an explanation in brackets. 2. One change at a time. If I ask for two, do the first and ask about the second. 3. Keep all game numbers in a CONFIG object at the top of the script, each with a comment. 4. After a change, open the game and write in one or two lines what I should notice. 5. Save only when I say “save”. Before saving, tell me which files changed. 6. Don't touch files outside this folder. Keep the notes to 30 lines or less. Show them to me in full.

Read what the agent wrote and cut repetition. The Claude Code docs suggest staying under 200 lines; our course target is 30.For this course, aim for about 30 lines.

Check that the notes are being read

Start a new chat. It won't have your old conversation, but the rules file is still there.

Type /clear to start a fresh chat in the same folder.

Type /new to start a fresh chat in the same folder.

Open a new session in the same first-game folder.

Send a short task without repeating the rules:

Make the run 20% faster.

Make the flight 20% faster.

Make the snake 20% faster.

Check whether the agent follows the notes without a reminder.

Ask it to write the notes and read them through. Then start a new chat and send the short task. After checking the result, undo the speed change and save the notes:

Undo that speed-up. Then save: “agent notes”.

How to check:

The agent answered in plain words
It changed one number in CONFIG
It told me on its own what to notice
Speed-up undone, notes saved

If the agent ignores the notes, ask: “Check the name of the rules file you read automatically, and rename my notes to match.”

How does a new chat find the rules for your game?

From the notes in the game folderYes. It reads them at the start of every chat, even a new one.
From its memory of the previous chatThat conversation isn't part of this chat. The rules need to be in a file.
Nowhere; you have to type them againAvoiding that repetition is why we left notes in the game folder.

Remix reels

Keep the base game and use the reels to choose a hero, setting, goal and new rule. Make the goal specific: collect 10 stars, for example. Give the rule a number too, such as triggering every 15 seconds. Spin again or lock a choice you like.

George Fan, who made Plants vs. Zombies, got hooked on custom Warcraft III maps, especially tower defense, where you build towers against crowds of enemies. And he figured: “if you had plants as towers they could be expected to stay in one place, and you could draw faces on them” (PC Gamer, 2010). The theme explained the rule. Look for a pair like that: a rocket gets a turbo, a ghost passes through its tail.

remix reelsSpin, lock, play the preview

Make a remix of the game: copy index.html to remix.html and change only remix.html. Look: the hero is a snail in a spacesuit, the world is space: a dark blue background, stars, asteroids instead of cacti. Goal: collect 10 stars. Stars hang at jump height, a big star count at the top. When the goal is done, show a “You win” screen. New rule: every 15 seconds gravity drops by half for 5 seconds; a second before that, the screen flashes light blue. New numbers go in CONFIG: starsToWin: 10, lowGravityEvery: 15, lowGravitySeconds: 5, lowGravityMult: 0.5. Open remix.html and tell me what I should notice in the first 20 seconds.

The prompt builds itself. Copy it: you'll need it in the next step.

Build a combination you want to try yourself.

Lock the choices you like and keep spinning the others. Play the preview at least once, then copy the task for the agent.

How to check:

The prompt has a hero and a world
The goal has a number
The rule has a number
The prompt is copied

If nothing appeals to you, take the example in the next step and change its hero or setting.

Send your idea to the agent

Now let's turn that idea into a game. The agent will make a copy in remix.html, leaving yesterday's version available for comparison.

Send the task from the reels or use this example:

Make a remix of the game: copy index.html to remix.html and change only remix.html. Look: the hero is a snail in a spacesuit, the world is space: a dark blue background, stars, asteroids instead of cacti. Goal: survive 60 seconds and collect 10 stars. Stars hang at jump height, a big star count at the top. New rule: every 15 seconds gravity drops by half for 5 seconds; a second before that, the screen flashes light blue. New numbers go in CONFIG: starsToWin: 10, lowGravityEvery: 15, lowGravitySeconds: 5, lowGravityMult: 0.5. Open remix.html and tell me what I should notice in the first 20 seconds.

Make a remix of the game: copy index.html to remix.html and change only remix.html. Look: the hero is a penguin, the world is a glacier: a light blue sky, snow, ice pillars instead of pipes. Goal: fly through 20 gates between pipes. A big gate count at the top. When the goal is done, show a “You win” screen. New rule: every 10 seconds the wind pushes the hero down for 3 seconds; before a gust, streaks fly across the screen. New numbers go in CONFIG: gatesToWin: 20, windEvery: 10, windSeconds: 3, windForce: 600. Open remix.html and tell me what I should notice in the first 20 seconds.

Make a remix of the game: copy index.html to remix.html and change only remix.html. Look: the hero is a delivery robot, the world is an office: the field is gray carpet, cups of coffee instead of apples. Goal: eat 15 cups of coffee in 60 seconds. The score and the time left, big at the top. When the goal is done, show a “You win” screen. New rule: every 5th treat is golden: for 5 seconds the snake moves twice as fast and points count double. New numbers go in CONFIG: foodToWin: 15, timeLimit: 60, goldEvery: 5, goldSeconds: 5, goldSpeedMult: 2. Open remix.html and tell me what I should notice in the first 20 seconds.

Eric Barone on Stardew Valley: “I decided to start with the basic Harvest Moon ‘formula’ and then expand on it in my own way” (Game Developer, 2017). A familiar base, your own details. Same with a remix.

Your remix goes in remix.html; index.html stays as it was.

Wait for the agent to finish, then play three rounds. If everything works, ask it to save:

It works. Save: “remix”.

How to check:

New hero and world are visible
The goal is counted on screen
The new rule kicked in within 30 seconds
index.html opens the same as yesterday

If the result doesn't match the task, look for a similar case in the table below.

what you see	what to tell the agent
the agent changed `index.html`, not the remix	“Restore index.html to the last save. Make the remix only in remix.html”
stars or rings are out of reach	“I can't reach them. Check that each one can be grabbed at the current speed, and fix it”
the whole remix broke	“Restore the last save. Do only the look. Goal and rule in the next prompts”
the new rule isn't noticeable	“Make the rule kick in first at second 5. Tell me what to watch”

Take one part away

Try the same experiment in your own game. Remove losing and play for 30 seconds. Notice whether you still bother avoiding obstacles, and when your interest starts to fade.

Remove losing from remix.html: touching an obstacle does nothing anymore. Don't save.

Remove losing from remix.html: touching a pipe, the ground or the screen edge does nothing anymore. Don't save.

Remove losing from remix.html: the snake passes through walls and through itself. Don't save.

Compare your runner with and without losing.

Play for 30 seconds, then put the original rules back:

Restore the last save.

How to check:

I compared the runner with and without losing
After “restore”, touching is dangerous again

If losing has not come back, ask: “Show me what changed since the last save, then restore all of it.”

Try a genre you like

This step is optional. If you have a genre in mind, try one change below in remix.html. The notes cover the usual rules. Haven't chosen yet? We'll come back to genres on day 4.

Add platforms at different heights and try jumping between them.

Add platforms at two heights to remix.html: rewards hang above the upper ones, and you can only reach them from a platform.

Let the hero move in every direction, with enemies approaching from different edges.

Make an arena mode in remix.html: the hero walks in all directions with the arrow keys, obstacles fly in from every edge, survive 60 seconds.

Start with tiles and one rule you can test.

Make an 8 × 8 tile field in remix.html: the hero moves tile by tile, and obstacles move after each of your moves.

Try choosing a card between rounds and see how it changes the next run.

After each round in remix.html, offer a choice of 3 upgrade cards: hero 10% faster, a shield for one hit, rewards ×2.

Try giving the hero orders instead of controlling every step.

In remix.html, control the hero with a mouse click: it walks to where you clicked.

Replace the risk of losing with something satisfying to collect and improve.

Remove losing in remix.html: a hit takes away one reward. Rewards add up between rounds, and the hero buys hats with them.

Add a short scene with a choice between rounds.

Before each round in remix.html, show a card with one line from the hero and a choice of two: the choice decides which obstacles the round has.

Try aiming and hitting a target.

Add a shot on the F key to remix.html: a projectile flies forward and smashes an obstacle. 5 ammo, and each reward adds one.

Let the hero grow stronger after a round.

In remix.html, give the hero experience for every obstacle passed and a new level every 10 experience points: +5% to the hero's main number, jump or speed.

Play with the change. Like it? Ask the agent to save “remix and genre”. Otherwise, restore the last save.

Play, check and save

Before saving the day, check the remix and answer a few questions.

The agent checks

Check: remix.html opens with no errors in the console, index.html hasn't changed since the last save, all the remix's new numbers are in CONFIG.

You play

Play three rounds. Can you understand the goal without an explanation? Do you notice the new rule?

★ Fresh eyes

Open a new chat, as in step 3. Have the agent check the files without your earlier conversation.

Read the notes and remix.html. List where the remix breaks the rules in the notes. Don't change the code.

Once the checks pass, save the day.

Save the day's version: “day 2: remix”. Add the tag day-02.

A friend asked for five changes at once and broke the game. Where should they start?

Restore the save and change one thing at a timeYes. Save after each change, and you'll see right away what broke the game.
Ask the agent to fix everything at onceThe agent would have to guess which of the five changes did it.
Delete the game and start againThere is already a working save. Restore it, then try the changes one at a time.

You can run and jump in the game, but there's no score and no finish. What is it?

A game without feedback: it needs a jump soundFeedback has nothing to do with it. The player has nothing to go for.
A finished game: running is already funFun for about ten seconds. Without a goal it's a toy.
A toy: it needs a goal with a numberYes. For example, “10 stars in 60 seconds”.

The notes have grown to 300 lines. What should you do?

Yes: more rules, a more precise agentThe opposite: the agent follows long notes worse.
No: keep only the rules you needYes. Only the ones the agent breaks without them. The course target is 30 lines or less.
Add headings but keep all 300 linesHeadings help you find rules, but the unnecessary ones are still there. Cut repetition first.

What can a remix take from someone else's game?

The rules and ideas of how it worksYes. We don't take someone else's art, heroes or name.
The hero art, if you change the colorWe don't take someone else's art, not even recolored.
The name, so people recognize it right awayThe name belongs to someone else. Come up with your own.

What changed in Vampire Survivors when the project came alive?

The rules: the author came up with a new weaponThe rules stayed. The art changed.
The art: vampires instead of placeholdersYes. Same rules, and the author wanted to work on the game again.
The engine: the author rewrote the game from scratchThe interview says nothing about that. The art changed.

homework · day 2

Five rounds and another player

must do

Play five rounds. Write down one number you'd like to change: speed, jump height or how often the new rule triggers. We'll use it tomorrow
Let someone else play and ask, “What are you trying to do here?” Listen without giving hints

extra credit

Remix a second cartridge: ask the agent to build another cartridge from Getting ready in a separate file, and remix it with the reels

for your genre

Find a reward you can barely reach. Would you rather jump higher or farther? Write it down.

Notice how long it takes for the screen to get crowded. That will help when we work on waves.

Come up with one tile rule that changes how obstacles move. Write it in one sentence.

Come up with three upgrade cards for the remix, each with its own number.

Imagine there are five heroes. What order would you give all of them?

Choose something you'd enjoy collecting in the remix and something to spend it on.

Write one line the hero says before a round: who they are and where they are going.

Choose what feels better to you: hitting a target or dodging. That can help you pick a core mechanic.

Write down which hero number should grow with each level: jump, speed or lives.

how to tell it worked

criteria	pass
Remix	new hero, world, goal and rule with numbers; `index.html` as yesterday
Agent notes	30 lines or less, the agent follows them in a new chat
Player	noted whether they got the goal without a hint

Time: 15–20 minutes.

remember

This runner has a goal, action, obstacle, feedback and an end. Switch them off one at a time to see what each contributes.
Keep agent notes short. Include the rules the agent needs for every change.
A remix keeps a familiar base and adds your choices. Describe the goal and new rule so you can check them in play.
It works: “save”. It broke: “restore the last save”.

Sources

Vampire Survivors creator didn't have a vision when he started making the game Rich Stanton, PC Gamer, 2022-03-30 · checked 2026-10-26
George Fan and his cat on the making of Plants vs. Zombies Graham Smith, PC Gamer, 2010-11-02 · checked 2026-10-26
Road to the IGF: ConcernedApe's Stardew Valley Alissa McAloon, Game Developer, 2017-02-24 · checked 2026-10-26
How Claude remembers your project: “target under 200 lines per CLAUDE.md file” Anthropic · checked 2026-10-26
AGENTS.md: “Codex reads AGENTS.md files before doing any work” OpenAI · checked 2026-10-26

Next lesson, we'll compare two versions that differ by a single number. Then we'll add a control panel so you can adjust your remix with sliders.