Ghastly kid, Unborn Val'kyr, Infected squirrel (breeds don't matter, since void gate either misses due to ethereal, or doesn't force a swap due to 2 pets being dead): Ethereal -> haunt (swap in val'kyr) -> Curse of Doom -> Unholy Ascension (swap in squirrel) -> Stampede. Since this is an undead team, you're even resilient againts unlucky crits due to the immortal round.
Great suggestions! However, almost all the guides for Fel-Beasts of Argus keep suggesting Infected Squirrel for the use of Stampede. I'm in the process of leveling mine but as others have suggested in different fights, you can easily sub Infected Squirrel with Macabre Marionette and use Dead Man's Party for the same move set. Just did this and it worked like a charm.