6.3.1 has that Medusa boss right? I'd recommend bringing a normal questing team that counters one of the paths and for the Medusa boss use AA and Yondu. She only takes damage from bleeds and neither gain buffs except from dex. Try not to dex her. For yondu I would spam like 6 sp1s because he places a heal block with that and then do an sp2 for the furies to make your bleeds more potent.Another boss option is Joe Fixit.Another option is use Void and heal reverse her to her death.
If you can manage to reverse the healing medusa will lose health every time buffet triggers.If bleed just doesn’t work out for you, you can try void… although it might end up taking more time