Spawns a friendly Jerkshroom that follows the player around.
If an enemy is nearby, it will charge at them, dealing a base 50 damage on impact.
If the enemy hits a wall after being hit, an additional base 100 damage is inflicted.
Attempting to summon the Jerkshroom again while it is still active will instead make it explode, dealing 300 base damage to any nearby enemy. The skill then goes on cool-down.
The Mushroom Boi is part of a sacrificial ritual that grants the player the Sacrificial Tick Outfit. To initiate this ritual, the player must go to the Morass of the Banished. In it, the player must reach the end of the biome, where a masked individual known as the Swamp Priest resides. The Swamp Priest stands next to an altar that depicts Mama Tick, he nags the player to offer a sacrifice, namely the Mushroom Boi. If the player complies and uses the skill again while the spawned Jerkshroom is active, it will jump onto the altar and explode while screaming "Why?" This removes the skill from the player's inventory and skips the subsequent fight with Mama Tick. This ritual can be repeated in subsequent visits with the same result, but the outfit can only be obtained the first time unless the player did not hand it over to the Collector.
If the player has a ranged weapon in their inventory and manages to attack Mama Tick in the brief moments she raises her eye above the water, the fight begins as usual and the outfit blueprint will not be dropped.
Synergies
As a pet, enemies thrown by the Hand HookTQatS will take critical damage if they collide with the Mushroom Boi!.
Mushroom Boi! intends to passively stun and push enemies away from the player providing distance and safety windows, this can, despite possibly mismatched scalings:
Satisfy the critical condition for Marksman's Bow, which "Inflicts a critical hit at long range."
Satisfy the conditions for the damage boost provided by Tranquility
Allow for synergies with a variety of long ranged and potentially slow weapons, such as, but not limited to:
The Mushroom Boi! will not attack nearby enemies if the player is invisible.
To obtain its relevant achievements:
Bound for Hell - Detonate the Mushroom Boi by using the skill again while Mushroom Boi is active.
Who's a good boi? - Beat the final boss while the Mushroom Boi is active, and do not detonate mushroom boi.
Pact with the Devil - Sacrifice the Mushroom Boi to Mama Tick, as mentioned in the previous section.
As a pet skill, Mushroom Boi! may stagger or displace enemies, changing proper timings and positionings in unpredictable ways, causing risk when parrying or using heavy short ranged weapons.
Trivia
The Mushroom Boi! is the second pet skill to be added to the game, with the first being the Great Owl of War.
It is so far one of the only items in the entire game that contains non-alphabetical characters in its name.
There is a visual glitch that occurs when you teleport anywhere and have activated Mushroom Boi! that makes him appear to be crouching, similar to the Jerkshroom Hide defensive ability.
Hand HookTQatS will take critical damage if they collide with the Mushroom Boi!.
Marksman's Bow, which "Inflicts a critical hit at long range."
Tranquility
Explosive Crossbow
Repeater Crossbow
Heavy Crossbow
Magic Bow
Nerves of Steel
Soul ShotFF
HemorrhageRotG
Great Owl of War.
Hattori's Katana, 
Scarecrow's SicklesFF, and 5BSC Spoiler SkillRotG
5 