Tunnel through the dirt, corner the creatures lurking underground, and pump them until they pop — keep clearing waves while the burrows fill up with faster threats.
Swipe up/down/left/right to dig and move. The first row is sky; everything below starts as dirt. You can move freely through tunnels you've already dug; entering a dirt cell digs it open. Tap on a monster that is in a cell directly adjacent to you to pump it once — four pumps in a row pop it for points. If you stop pumping a monster, it slowly deflates back. Touching an un-inflated monster costs a life. Clear all monsters on the board to advance with a faster wave.
Shape your tunnels with kill positions in mind. A dead-end of 2 cells lets you back into and pump a chasing monster safely — the monster cannot pass through you, and you have a wall behind you so it can't ambush from there.
Deeper kills score more (bonus per row of depth). When a monster wanders to the bottom of the board, tunnel down to meet it instead of luring it up — same number of pumps, double or triple the points.
Don't over-dig early. Every tunnel you cut becomes a path the monsters can use, and they get faster every wave. Leave intact dirt walls between yourself and far-side monsters so the AI has to take long routes around to reach you.
A partial inflation is still useful. Even one pump slows the monster's deflation timer briefly, buying you time to reposition. If you're cornered and can't get four pumps in, one pump can still save you long enough to escape down a side tunnel.