Played on PC.
Boss: Grim Matchstick
Loadout: Charge, Peashooter
Charm: Whetstone
The Cuphead Souped Up mod is an incredibly difficult Cuphead mod that gives bosses some new attack patterns, makes them faster, and gives them way more health. There's also a stat rebalance of the weapons in the game to nerf some of the most powerful weapons and buff some of the under utilized weapons to allow more versatility in weapon choice for each boss.
Grim Matchstick is a work of art in this mod. The mod creator did was I thought they should've done in the vanilla game and actually made it so that the clouds reverse direction for final phase. They also took away the randomization of the clouds and made them repeat in a particular pattern so you don't wind up at the mercy of RNG platforms with nowhere to go. Very fun fight! This might be my favorite out of the whole mod.
The mod can be downloaded here: bit.ly/cup_mod -- Watch live at / jason2890