Splat your biomass across the board, drop defenders on top of it, and match their color to whatever the tide sends at you. Enemies only pay when they die on your biomass - in the color they die on.

Upgrade between waves, hold out against Karkinos, and see how far you get. All of it in 64x64 pixels. Press below means click or tap; nothing in the game needs a keyboard.

THE GOAL

Your tower stands on the board - in a corner, on an edge, or dead center, depending on the map. The tide attacks it in waves, and each wave is bigger than the last. Keep the tower standing: the run lasts exactly as long as it does.

An enemy that reaches the tower deals damage equal to its remaining health, and dies there. Every hit rots a few more of the tower's 64 pixels. The damage is permanent, and at full rot the run is over - you read the tower's health off its sprite, and the more pink it shows, the closer the end.

1. SPLAT YOUR BIOMASS ACROSS THE BOARD

Drag to lay down colored ground - your biomass. A splat costs a sliver of the color you lay, and it only sticks where it touches biomass you already hold, so yours grows outward from the tower. It never fades on its own; only the wrecker, the scourer and Karkinos strip it (see THE ENEMIES).

2. DROP DEFENDERS ON TOP OF IT

Press the square in the top-right corner, pick one, press the board. Three kinds, on keys 1, 2 and 3 (see THE DEFENDERS).

A defender takes the color of the biomass you set it on - and a marked enemy takes damage from one color only, the one it wears. Matching is the whole fight.

3. HOLD BACK THE TIDE

The tide comes in from every side, loosely following the lanes. Any enemy that passes close to a defender aggros onto it and stops there - that is how you choose where a fight happens. Kill the wave's leaders and the swarm stops coming; when the board is clear, the wave ends.

Six enemy types, from a one-pixel swarm to the boss (see THE ENEMIES).

4. KILLS ON YOUR BIOMASS PAY

You open with 6. An enemy pays its bounty in the color of the biomass it died on, and pays nothing on bare board. The ring at the tower's feet cannot be stripped or painted over, so kills at home always pay.

Between waves a receipt prints what each species paid and what you spent, and clearing pays +1.

5. THE SECOND COLOR

You hold two colors, and you start with only the first. From wave 12 a mark can name the one you have not bought yet - and against a mark you cannot match, none of your defenders do any damage. That is the clock on it.

The second costs 8 of the first and then earns at half the rate. It buys the lure outright, and it is the main price on nearly every upgrade (see UPGRADES).

THE DEFENDERS

  1  costs 3 - the shooter. Fires from a third of the board away, but only stands on biomass of its own color - painting that color is how you extend its ground.

  2  costs 4 - the brawler. Hits everything in reach at once, three times as hard as the shooter, and roams its own color's ground looking for a fight.

  3  costs 1 of the second color - the lure. Never fights. Pulls enemies toward itself from half the board away and decides where a fight happens instead of winning one. Caps at four; each one standing prices the next higher.

You can field nine at once; the cap grows by one every ten waves, and prices creep up on the same clock. The number keys 1 2 3 arm a defender without opening the tray. The tower also drips free one-pixel drifters of its own - the little swarm at your feet is yours. Press the tower for the codex: a card on every unit and enemy.

THE ENEMIES

The number beside each is its bounty - what it pays dying on your biomass.

  THE BROOD    0.1 - a swarm. One pixel each, dozens at a time, and they only ever pay the first color.

  THE HERALD   1   - hugs the lanes, lends its color to enemies near it.

  THE WRECKER  0   - ignores your tower. Eats a channel through your biomass.

  THE SCOURER  0   - scrubs your biomass back to bare board, in straight lines.

  THE BULWARK  1.5 - frontal armor, facing you. Flank it.

  KARKINOS     5   - the boss. Wave 20, then every 5, and marked. Lobs shells, sheds brood - and if it reaches your tower, the run ends on the spot.

Karkinos arrives marked, and a herald's whole pack answers to its flag. A defender matched to the mark pulls twice as hard.

UPGRADES

Bought between waves, priced in competing colors - so what you paint is your build order. And with the roster capped, upgrades are the only way your defense keeps growing.

3 PLAYABLE GAME BOARDS