Any tips on fighting Buttercup?

[Captain Toast]

Or expedition bosses in general. I mostly go in solo.

I only recently hit level 50 and I mostly use a Combat Shotgun and a .44 Revolver that has armor piercing, and I have a rocket sledge for melee.

Are there any specific damage types I should use or specific weapons I should go after?

[Mooman]

VATs and crits. Revolvers and shotguns are high crit damage weapons that will bypass damage reduction (Buttercup is the PA guy?).

[Ember230]

go in with a team of flamers

[Wack-A-Mole MLRS]

The only time I am far enough away form the enemy to use VATS is if I'm doing a Double tap as I walk away from their dead body,

[Neotropic]

Holy Fire FTW!! :)
I feel bad when I see these. I breeze through it. Buttercup dies easily for me, solo or on team, PA or non-PA. I just kill the other mobs just for the hell of it and ammo.

[Wack-A-Mole MLRS]

Buttercup never dies-He gives up and runs away like Melted Butter.