PS Spectral Spinner worked. Zomstrok in slot 2 instead of Spirit Crab which I didn't have levelled - cast Shell Shield and Toxic Skin and refresh one round before they drop off and use Infected Claw as filler. My Zomstrok managed to finish the fight without needing to bring in the last pet.
Mr. Bigglesworth (2,1,2) also worked in slot 1: Ice Barrier > Pass > Howling Blast > Pounce until enemy 1 dies. Howling Blast > Pounce until dead
Zomstrok H/P (1,1,2) in its place. Kept Shell Shield and Toxic Skin active with Infected Claw as filler
Spirit crab with surge and you WON
I didn't have the crab leveled and the alternative strats failed repeatedly so I tried Grotesque in the 2nd slot (2,2,1) and only needed 2 bolts from my fragment to finish off the last pet. Keep Agony up/bolt - heal when at half health (2nd pet should almost be dead) and finish with Fragment of Anger once Grotesque dies.
I would recommend "Snap plus Whirlpool until Spirit Crab dies". I was able to get 2 Whirlpools off before my crab keeled over. Made a difference. When Fragment of Anger came in, he only had to do ~250 damage.