Alpine Chipmunk S/B (NutBarrage/AdrenalineRush/Woodchipper), Auburn Ringtail S/S (PoisonFang/Bite/Survival), and Grassland Hopper S/B (Screech) worked well for me. They managed to be speedier than Retch (either naturally or with spells). I'm sure that helped.
If you have them, S/S Grizzly Squirrel and S/S Gleamhoof Fawn have more power than the pets mentioned while still being faster. Grizzly can do two woodchippers before going into stampede for some more damage. Enemy died from the woodchipper tick after Fawn's headbutt, game over.