The Greezak Shoulder Cannon does not work like any other items in the game.

For instance, when a player wears a greezak shoulder cannon, their punch effect changes to that of the greezak shoulder cannon. However, if the player wearing greezak shoulder cannon wears another item, say Diamond Devil Horns, the punch effect will remain the same to that of the shoulder cannon instead of the thunder effect from the Diamond Devil Horns.

I believe this needs some looking because even though the greezak shoulder cannon has good visual effects, it dominates some other items’ cool visual effects.