A very unstable variety of mushroom that explodes when threatened.
Boomshrooms are individually weak but fast and extremely numerous: though they only have 75 HP and no resistance, they usually come in huge groups of 10 or more, making Druids essential to deal with them.
However, the real danger comes when they are killed. When killed or blocked, Boomshrooms violently explode, dealing 20 area damage in an area. While 20 damage might not seem that much, Boomshrooms are extremely numerous, so the damage can quickly rack up - enough to kill soldiers and heroes if you aren't careful.
Weirdwood is the bane of Boomshrooms: a single nut is almost guaranteed to instantly deplete the mushrooms' low health count, and Clobber, even at tier 1, can squash multiple of them at once. The Boomshrooms' relatively average speed would not allow them to dodge pass the deadly nuts.
In times of emergency, one can deploy units to block the Boomshrooms and sponge the damage from explosions, however even Forest Keepers can only take on a limited number of mushrooms before dying, thus beware.