Guide 12 — Roach Invasion

Joshua Freeman

What you're building

A 2D collectathon platformer. You switch between four insects with different abilities and health, evading mutated cockroaches and collecting all the plant-based items — picking whichever bug suits each enemy and hazard.

Your build has one thing nobody else's does: four playable characters with separate health pools. When one insect runs out, you switch to another; when they're all down, you respawn. That changes how death is wired, so read section 3 carefully.

Your sketch has HP written on each bug — 5, 3, 2, 3. Those go straight into the character assets.

Time: about three hours.

1. Before you start

• Finish Guide 0.
• Read Guide B §B1 (player) and §B4 (enemies).
• No new input actions — swapping uses the built-in Previous / Next (Q and E).

2. Scripts you'll use

Core — Guide B
PlayerController2D · PlayerAnimatorBridge · Health · DamageOnContact · Checkpoint · RespawnManager · CameraTargetAssigner · SceneLoader · GameManager · AudioManager · HUDController · MovingPlatform · ParallaxBackground

Collectibles
ItemType · Collectible · CollectionTracker

Enemies (Tier 2)
EnemyPatrol · EnemyChase · FloatingEnemy · Hurtbox · Hitbox · Knockback

Movement (Tier 3)
DoubleJump · Glide · Ladder + LadderClimber · CharacterDefinition · CharacterSwapper

Level (Tier 4)
SpikeTrap · KillZone · Door · LevelExit

3. How character swapping actually works

Read this before building anything — it's not what most people expect.

You do not make four player prefabs. You make one player object that carries every ability component, and a CharacterDefinition asset per insect that says which abilities are switched on, what the stats are, and which animator to use.

Why: four separate prefabs would each need their own camera target, PlayerInput, respawn wiring and hurtbox. Swapping between them means re-pointing all of that every time. One object with toggled components avoids all of it.

The death wiring is different for you

Every other guide wires Health.OnDied → RespawnManager.OnPlayerDied. You don't.

Health.OnDied → CharacterSwapper.OnCurrentCharacterDied
RespawnManager.OnRespawned → CharacterSwapper.ReviveAll

When an insect's health hits zero, CharacterSwapper marks that one down and switches to a living one. Only when all four are down does it call RespawnManager itself. Wire it the normal way and you'll respawn on the first insect's death, which throws away your entire mechanic.

4. Build the one player object

Follow Guide B §B1, but with every ability component attached. Most will be disabled at any moment — that's correct.

1. Empty GameObject Player, Tag → Player, Sprite Renderer.
2. Rigidbody2D (Gravity Scale 3, Freeze Rotation Z, Continuous), Capsule Collider 2D.
3. Player Input — Behavior: Send Messages.
4. PlayerController2D + GroundCheck child + Ground Layer.
5. Health — the values get overwritten per character, but set Invulnerability 1.
6. Animator + PlayerAnimatorBridge.
7. Knockback.
8. All the ability components, in any order:
   • DoubleJump
   • Glide
   • LadderClimber
   • (add Dash too if you want one insect to have it)
9. CharacterSwapper — configure in section 6.
10. Child Hurtbox — trigger collider, Hurtbox (Team = Player), layer Hurtbox.

After step 8 the Inspector will look crowded and several components will be greyed out during play. That's the design working.

5. Create the four insects

Right-click in Project → Create → GAME1303 → Character, four times.

The Enabled Abilities list holds component type names as text — spelling and capitals must match exactly.

Beetle (the tank — 5 HP)

Mantis (the climber — 3 HP)

Bee (the flier — 2 HP)

Ant (the all-rounder — 3 HP)

The animator trap

If you make four Animator Controllers, they must all use the same parameter names (Speed, IsGrounded, YVelocity, Jump). CharacterSwapper swaps the whole controller, and parameter values only carry across if the names match. A typo means the animation silently resets on every swap.

Simplest safe route: build one controller, then duplicate it three times and only change the clips. The parameters come along for free.

6. Configure the swapper

On Player, fill in CharacterSwapper:

Separate Health Per Character ✓ is your mechanic. Each insect keeps its own health, and a dead one can't be selected until you respawn.

Optional: add Character1–Character4 button actions to your input asset (bound to keys 1–4) if you want direct selection alongside Q/E cycling. The swapper listens for them automatically if they exist.

7. Build the level

The collectibles

1. Right-click Project → Create → GAME1303 → Item Type, name it Plant. Score Value 10.
2. PlantPickup prefab: sprite + trigger Circle Collider 2D + Collectible (Item Type → Plant, Bob ✓).
3. Place them everywhere — that's your game.
4. CollectionTracker in the scene.

The roaches

Your pitch says mutated cockroaches, and your sketch shows a "stinky" one.

Ground roach — Guide B §B4 with EnemyPatrol (Sensors mode), Health 2, Hurtbox (Team Enemy), BodyHitbox (Damage 1, Repeat Delay 1).

Flying roach — Rigidbody2D Gravity Scale 0, FloatingEnemy (Path Wander, Wander Radius 4, Bob Height 0.3), plus EnemyChase (Movement Free, Detect 6, Speed 3). Hurtbox and BodyHitbox as above.

Stinky roach — a ground roach with a big trigger child that has DamageOnContact (Damage 1, Repeat Interval 1). The cloud is the threat, not the body — that's a hazard your bee can fly over and your beetle can't.

Level furniture

• Ground on Ground with colliders
• KillZone underneath
• SpikeTraps (Guide 1 §6e recipe) — Damage 1, not Instant Kill
• Ladders: a sprite + trigger Box Collider 2D covering the full climb + the Ladder component
• Checkpoints
• A Door requiring all plants, in front of the exit
• LevelExit beyond it
• Camera per Guide B §B3

Gate the exit on collecting everything

On the Door:

Add a trigger child and drag it into Proximity Zone so it checks as you approach. Wire OnOpenFailed to a sound so a short player gets told, not just blocked.

8. The HUD

You need more here than most guides, because the player has to see four health pools.

1. Canvas → PortraitImage (Image) showing the current insect.
2. NameText (TMP) showing its name.
3. A health bar Slider or hearts.
4. PlantText (TMP) — Plants: 0 / 20.
5. Empty child HUD with HUDController:
   • assign the health bar or hearts
   • Item Counters → one entry: Item Type Plant, Text PlantText, Format Plants: {0}

Showing which insects are still alive

The nicest version is four small portraits in a row, greyed out as each falls. That needs a short script — worth asking for, since it's the readout your mechanic depends on. A simpler stand-in: OnCharacterChanged swaps the single portrait, and the health bar shows only the current insect. That works, it just hides how much reserve you have left.

9. Wire it up

Rows 1 and 2 are the ones to double-check. Row 1 must go to CharacterSwapper, not RespawnManager — that's the difference between your game and a normal platformer.

10. First playtest

Build a small room with a ladder, a gap the bee can glide over, and two roaches.

1. You start as the Beetle with 5 health.
2. Q and E cycle through the four insects.
3. Each insect has different stats — the bee should visibly float more (Gravity Scale 1.5).
4. The bee can glide (hold Jump while falling) and the beetle can't.
5. The mantis and bee can double jump; the beetle and ant can't.
6. Every insect can climb the ladder except any you left LadderClimber off.
7. Damage only hurts the current insect — take a hit as the Ant, swap to the Beetle, confirm the Beetle still has 5.
8. When an insect hits 0, you auto-swap to a living one rather than dying.
9. A dead insect can't be selected — cycling skips it.
10. When all four are down, you respawn at the checkpoint with everyone revived.

Steps 7–10 are the whole build. Test them deliberately: drop three insects on purpose and confirm the fourth is still playable, then drop the fourth and confirm you respawn.

11. Then add

1. Level design that needs the swap. Right now the insects are different; make them necessary. See the design notes.
2. Animation — four controllers, identical parameters. Guide B §B6.
3. A Dash insect if you want a fifth ability — add Dash to the player and list it on one character.
4. ParallaxBackground — grass and stems in layers.
5. A second level with a different plant count.
6. Sound: a distinct swap sound, per-insect footsteps if you're ambitious.

12. Design notes for your game specifically

Right now you have four insects. Make them four keys. The mechanic only sings when the level asks for a specific bug:

• A gap only the bee can cross (glide)
• A crushing hazard only the beetle survives (5 HP)
• A high ledge needing the mantis (double jump)
• A narrow tunnel where the tanky beetle is too slow to escape a chasing roach

One of each of those makes the swap essential. Without them, players find a favourite and never switch — and your whole design becomes a character-select screen.

Separate health is a resource, not four lives. The interesting decision isn't "which bug do I like," it's "the bee is on 1 HP and there's a flying section coming — do I use her now or save her?" Make sure there's at least one section per level where a specific insect is needed, so spending them carelessly has a cost.

2 HP on the bee is right. She has the most useful ability and the least durability. That's the trade that makes gliding feel like a decision instead of a free upgrade. Don't be tempted to buff her.

Collectathon means the level is the content. Your systems will be done after section 8. Everything after that is placing plants in interesting places — behind a glide, above a double jump, past a hazard only the beetle survives. Every plant should be a small question about which bug to use.

Watch out for softlocks. If a plant is behind a bee-only glide and the bee is dead, the player is stuck until they respawn. That's usually fine — respawning revives everyone — but make sure a checkpoint is reachable from anywhere. Test this specifically.

13. Common problems

14. Checklist

• One player object with all ability components attached
• Four CharacterDefinition assets with health 5 / 3 / 2 / 3
• Enabled Abilities spelled exactly as the component class names
• CharacterSwapper with Separate Health Per Character ✓
• Health.OnDied → CharacterSwapper.OnCurrentCharacterDied
• RespawnManager.OnRespawned → CharacterSwapper.ReviveAll
• Four Animator Controllers with identical parameter names (or none yet)
• Plant ItemType + pickup prefab + CollectionTracker
• Three roach types including a flier
• Ladders, spikes, kill zone, checkpoints
• Door requiring all plants, in front of the exit
• At least one section per insect that needs that insect
• Steps 7–10 of the playtest all pass