Quicksand

Quicksand is a new terrain type in the next Bloons Tower Defense game. It is possible to put land or water towers onto it. However, any towers that are placed on it will slowly sink into it, eventually being destroyed. In general, this takes a while, but the actual length of time it takes depends on the type of the tower. When towers are close to sinking all the way into it, their attacks will be less powerful.