Played on PC.
Boss: Root Pack
Loadout: Peashooter, Spread
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.
Root Pack is a great first boss of the mod, because it really shows you what this mod is all about without giving you an insurmountable challenge right from the start. Root Pack is tough, but fair.
The mod can be downloaded here: bit.ly/cup_mod -- Watch live at / jason2890