Tower Devouring

A worm beneath the arena devours your towers. From wave 6 on, at the end of a wave it may drag some of them underground. Which ones is pure chance -- no tower is safer than another -- and it never takes two that stand side by side.

How many grows with the run: one up to wave 10, two up to 20, three up to 30. You cannot prevent it, but you can plan for it: keep your maze from depending on any single tower, and keep gold aside to rebuild. A card can raise the risk in exchange for a reward.

What it drags down leaves WRECKAGE behind: the tower's remains stay on the tile and nothing can be built there until they are cleared. Only the Collector clears them, from its first level. Insects walk over wreckage without losing any time, so a devoured tower opens a shortcut through your maze.