Head Smack: The Shroom smacks its head into the player.
Toxic Fumes: When on low health, they can release toxic fumes that linger for a short amount of time.
There are two ways to fight Shrooms. One way is to use hit-and-kite technique where you hit them and back up when they prepare to attack you. Another tip is circling around the Shroom preventing them from hitting you in the right orientation.