Mushroom Guy (its a really cool guy) is a hostile mob which is a Mushroom (not to be confused with Red Mushroom) with a notable size increase as well as the addition of legs and arms. He has a distinctive green glow which can be seen from across the map, as well as from outside of the caves from which he spawns.
Mushroom Guy is hostile, and will attack the player only when in very close proximity for 5 hitpoints at a time. He makes no noise, has no animations, and will simply "glide" towards the player. He also lacks the capability to jump, and loses aggro very quickly.
When not attacking the player, he will occasionally move small distances. It is unlikely he will stray very far from his cave. Mushroom Guys can only be found in caves in Grassland biomes, and will spawn one at a time (once per season.)
Upon death, Mushroom Guys drop 3 Mushrooms.
Mushroom Guy's damage output is quite manageable, and will drop 3 Mushrooms, giving the player 50 health each when consumed for a total of 150 health, which is generally more than enough to completely negate the damage taken if attacked with a melee weapon.
The 3 Mushrooms dropped by Mushroom Guy can act as a very reliable staple.
3 Mushrooms is all it takes to create a MaxHealth Potion, although it is a bit redundant considering the Mushrooms will likely already heal more than the player's maximum health. However, the MaxHealth potion is very reliable as a blessing because of its prevalence paired with its yield in the Sacrificial Meter.