"I'm a singin' salmon, Spendin' all day jammin" ― Singin' Salmon, Gravity Falls
The Holy Mackerel is a melee weapon for the Flanker and takes the appearance of a fish. This weapon is a reskin of the stock Bat, meaning it doesn't have any special stats beside for telling the enemy you don't take anything seriously, after all you're beating them to death using a fish.
Unlike its TF2 counterpart (which also has the same name), the Holy Mackerel doesn't have jiggle bone physic, due to Roblox's engine limitation. Also, it does not have the "FISH KILL!" statement in the killfeed upon eliminating an enemy.