Levelling Up Speed — Scratch L2

Where this arc is heading: the fall-speed watcher climbs as the Score grows, and the kuih visibly drop faster. The game gets harder the better you play — the secret of every arcade game.

Learning Goals 3 min

By the end of this lesson you will be able to:

Create a fall-speed variable, set its starting value, and tick the box that shows it on the Stage so the player watches it climb.
Use the () mod () operator with if <> then to fire a milestone every few catches.
Replace a hard-coded change y by (-5) in the kuih clone with change y by ((0) - (fall-speed)) so kuih fall faster the moment fall-speed changes.

Warm-Up — the game that never gets harder 7 min

You finished L02-39 with a Catch the Kuih game that works — kuih fall, score climbs, lives drain. Aisyah's little brother played it after class. He scored 42 on his first try.

Open last lesson's clone-mover. It looks something like this:


when I start as a clone
go to x: (pick random (-220) to (220)) y: (170)
show
repeat until <(y position) < (-170)>
  change y by (-5)
  if <touching (Basket v) ?> then
    change [score v] by (1)
    go to x: (pick random (-220) to (220)) y: (170)
  end
end
change [lives v] by (-1)
delete this clone

The kuih clone falls at a fixed 5 pixels per frame. Always.

Click the flag and play for thirty seconds. Then for two minutes. Then for five.

Reveal — what's wrong

Nothing changes. Minute one is exactly as hard as minute five. The game has no arc. Once you've figured out how fast to slide the basket, you can play forever without losing. Real arcade games — Pac-Man, Tetris, Flappy Bird — get faster as you score. That keeps you leaning in. Today we add the arc.

The trick is one little variable, fall-speed, that changes itself whenever the player hits a milestone.

New Concept — a variable that grows with the score 15 min

Until now, the 5 inside change y by (-5) has been a hard-coded number — typed straight in, never changing. Today we replace it with a variable, then slowly raise that variable while the game plays.

Step one — a new variable

Open the orange Variables palette. Click Make a Variable. Name it fall-speed. Make it For all sprites — the kuih clones need to read it. Tick its checkbox so it shows on the Stage as a watcher. Watching the number tick from 5 to 6 to 7 is half the fun.


when flag clicked
set [fall-speed v] to (5)

On the Stage (or the kuih sprite — either works). Every new game resets the difficulty back to easy.

Step two — use the variable in the fall

Inside the kuih clone, swap the hard-coded -5 for the variable. Scratch has no "negative variable" block, so we subtract the variable from zero:


when I start as a clone
go to x: (pick random (-220) to (220)) y: (170)
show
repeat until <(y position) < (-170)>
  change y by ((0) - (fall-speed))
  if <touching (Basket v) ?> then
    change [score v] by (1)
    go to x: (pick random (-220) to (220)) y: (170)
  end
end
change [lives v] by (-1)
delete this clone

The kuih now falls at whatever fall-speed currently is. Change the variable, the kuih obey.

Click the flag. The game plays exactly as before — kuih drop at 5 pixels a frame. Good. We haven't broken anything; we've just made the speed changeable.

Step three — the milestone trigger

Now the part that makes the variable climb. Every five catches, fall-speed goes up by one. The block that asks "is the score a multiple of five?" uses the mod operator from the green Operators palette:


if <((score) mod (5)) = (0)> then
  change [fall-speed v] by (1)
end

"If the score divided by 5 leaves no remainder, bump the speed by one." So at score 5, 10, 15, 20… the kuih speed up.

What is mod? It's the leftover after division. 17 mod 5 is 2 (5 goes into 17 three times with 2 left). 20 mod 5 is 0 (no leftover). So (score) mod (5) = 0 is true exactly when the score is a multiple of 5 — every 5th catch.

Worked Example — adding speed-up to last lesson's game 12 min

Open your SCR-L02-39 Catch the Kuih project. We upgrade it in eight steps. Save a copy first if you are nervous — call it L02-40-Speedy.sb3.

Stage plan. The fall-speed watcher climbs as catches build; the milestone check lives on the basket (the ✏️ target today), right where the score changes.

Step 1 — Make the fall-speed variable

Variables palette → Make a Variable → name fall-speed → For all sprites → OK. Tick the checkbox so the watcher shows on the Stage.

Step 2 — Initialise it at the flag

On the Stage (or the basket — either is fine, pick one), add:


when flag clicked
set [fall-speed v] to (5)
set [score v] to (0)
set [lives v] to (3)

Every flag-click resets all three game variables. fall-speed joins the gang.

Step 3 — Switch the kuih to use the variable

Click the kuih sprite. Find the clone's repeat-until. Replace change y by (-5) with change y by ((0) - (fall-speed)). Use the green () - () block, with a literal 0 on the left and the fall-speed reporter on the right.

Step 4 — Test that nothing's broken

Click the flag. Play 10 seconds. Kuih should fall at exactly the old speed — because fall-speed sits at 5, the same as the old hard-coded number. If kuih fall up, you put fall-speed on the wrong side of the minus.

Step 5 — Find where score changes

Click the basket sprite. Find the catch script. It probably has a touching-the-kuih check that bumps the score:


when flag clicked
forever
  if <touching [Kuih v] ?> then
    change [score v] by (1)
  end
end

If your scoring lives on the kuih clone instead, that is fine — just add the milestone check right after the score-bump there. One milestone per catch is what matters.

Step 6 — Add the milestone check

Right after change [score v] by (1), drop in a new if-then that uses mod:


when flag clicked
forever
  if <touching [Kuih v] ?> then
    change [score v] by (1)
    if <((score) mod (5)) = (0)> then
      change [fall-speed v] by (1)
    end
  end
end

Catch a kuih → score +1. If the new score is a multiple of 5, fall-speed also +1.

Step 7 — Play and watch the watcher

Click the flag. Watch the fall-speed widget. At 5 catches it jumps to 6 and kuih drop quicker. At 10: 7. At 15: 8. By 30 catches the kuih are fast.

Step 8 — Add a tiny celebration

Optional but lovely. Inside the milestone if-then, before the speed bump, add a quick sound so the player gets feedback they unlocked a new level:


if <((score) mod (5)) = (0)> then
  play sound [Magic Spell v] until done
  change [fall-speed v] by (1)
end

A little ping every milestone. The player learns to expect it.

The full assembled stack — on the basket


when flag clicked
forever
  if <touching [Kuih v] ?> then
    change [score v] by (1)
    if <((score) mod (5)) = (0)> then
      play sound [Magic Spell v] until done
      change [fall-speed v] by (1)
    end
  end
end

The basket's catch-and-level-up brain. One nested if-then, and now the game has an arc.

What you just built: the difficulty curve. Every arcade game you've loved has one. You now know how to add one to any of yours: one variable, one mod-based milestone, one change.

Try It Yourself — three difficulty-scaling drills 15 min

🟢 Easy

Goal: Change the milestone from "every 5 catches" to "every 3 catches". The game ramps up faster. Make exactly one change.


if <((score) mod (3)) = (0)> then
  change [fall-speed v] by (1)
end

One number changed: the 5 became a 3.

Think: Mod is your dial. mod 3 means "every third catch". mod 10 means "every tenth — gentler arc". Same code, totally different feel.

🟡 Medium

Goal: Cap the speed. Right now fall-speed grows forever and the game becomes impossible. Add an if-then so it stops climbing after 12.


if <((score) mod (5)) = (0)> then
  if <(fall-speed) < (12)> then
    change [fall-speed v] by (1)
  end
end

Nested if-thens. The outer fires every milestone; the inner only bumps when there's room.

Think: Even the toughest arcade game has a max difficulty. Capping the variable makes a game punishing but fair.

🔴 Stretch

Goal: Add a second knob — spawn-wait. The kuih spawner waits a fixed time between drops; make the wait shrink as the score grows. Start at 1.5, drop a kuih every spawn-wait seconds, shrink by 0.1 every 5 catches (floor 0.3).


when flag clicked
set [spawn-wait v] to (1.5)
forever
  create clone of [myself v]
  wait (spawn-wait) seconds
end

On the kuih sprite. The wait is now a variable, not a hard-coded number.


if <((score) mod (5)) = (0)> then
  change [fall-speed v] by (1)
  if <(spawn-wait) > (0.3)> then
    change [spawn-wait v] by (-0.1)
  end
end

On the basket's milestone block. Two knobs turn at once: kuih fall faster and arrive more often.

Think: Real designers tune three or four knobs at once — speed, spawn rate, enemy count, score multiplier. Same pattern, repeated. You've built a tunable game, not just a faster one.

Mini-Challenge — the speed-up that fires too often 5 min

"Priya's runaway kuih"

Priya copies the lesson code and tests. After two catches, her fall-speed watcher reads 87. The kuih are a vertical blur. She shows you this script on the basket:


when flag clicked
forever
  if <touching [Kuih v] ?> then
    change [score v] by (1)
  end
  if <((score) mod (5)) = (0)> then
    change [fall-speed v] by (1)
  end
end

Priya's stack. Looks almost identical to the lesson — but read it carefully.

The score is 5 (or 0, or 10…). What does the milestone check do? How often?

Reveal one valid solution

The milestone check is outside the catch if-then. So it fires every frame of the forever loop, not just when the score changes. The moment the score is 5, the milestone is true — and stays true while the score is 5. The forever runs ~30 times a second, so fall-speed gets bumped ~30 times a second until the score finally ticks to 6.

Also: at the very start, score is 0. And 0 mod 5 = 0 is true! So Priya's fall-speed is bumped ~30 times per second from frame one, before she catches anything.

The fix is to nest the milestone check inside the catch if-then, so it runs at the moment a catch happens — exactly once per catch:


when flag clicked
forever
  if <touching [Kuih v] ?> then
    change [score v] by (1)
    if <((score) mod (5)) = (0)> then
      change [fall-speed v] by (1)
    end
  end
end

Same blocks. Different nesting. The fence between "always check" and "only check when something happens" is the whole game. Where you put the if-then matters more than what's inside it.

Recap 3 min

You added a difficulty curve. A new variable, fall-speed, replaces a hard-coded number in the kuih's fall script — now changing the variable changes how fast they drop. A milestone check using () mod () fires every Nth catch and bumps the variable. The watcher on the Stage shows the climbing number. The same pattern — one variable, one milestone, one bump — scales to spawn rate, enemy count, every difficulty knob in arcade games.

Difficulty scaling: Making a game get harder as the player gets better. The arc that keeps arcade games addictive.
Hard-coded: A number typed straight into a block (like -5 in change y by (-5)) that can't change while the game runs. The opposite of a variable.
Mod (modulo): The leftover after division. () mod () in Operators. (score) mod (5) = 0 is true exactly when the score is a multiple of 5 — the classic "every N" trigger.
Watcher: The little box on the Stage showing a variable's value. Tick the checkbox by the variable name to turn it on.
Milestone: A score (or time, or count) at which something special happens. Today's milestone: "every 5 catches → speed up".

Homework 2 min

The Tuner. Build a tuned version where the difficulty arc feels just right — not too easy, not impossible.

Open today's L02-40 project. Save as HW-L2-40-Tuner.sb3.
Change the milestone from mod 5 to mod 3, mod 7, and mod 10 in turn. Play each a minute. Pick the best.
Cap fall-speed at 10 (see the Medium task). Make sure the watcher actually stops climbing.
Add a starting speed of your choice — 3 for "chill mode", 8 for "panic mode". Reset to it at the flag.
Show say [LEVEL UP!] for (1) seconds on the basket every milestone, before the speed bump. Make sure it doesn't fire 30 times a second (re-read the mini-challenge).

Save your final tuned version. Play three minutes straight. Note your highest score.

Bring back next class:

Your HW-L2-40-Tuner.sb3.
Your highest score, the milestone you chose (mod 3, mod 5…), and one sentence on why it felt best.
Your answer to: "What's one other variable in this game that could get harder as the score grows, besides fall-speed?"

Heads up for next class: SCR-L02-41 · Catch the Kuih is the arc finale Build lesson. You'll polish the whole game into a portfolio piece — kuih sprites, a basket you control, a Score+Lives HUD, the speed-up, a game over and a title — then save and share it.