Growing Ectoplasm

Challenge Mode
Zandalari Anklerender 2-1-2 or Zandalari Kneebiter 2-2-1
Black Claw
Hunting Party
Leap til Boss dead
Clean up with what ever pet you want I used the same Emerald Proto-Whelp 2-2-2 for all 12 fights for clean, just keep healed up before killing last pet

Mechanical Pandaren Dragonling was what I had to use to get him down.

I used Sprite Darter Hatchling (2-2-1), Onyxian Whelpling (2-1-2), and Emerald Whelpling (1-2-2). Dream Whelpling and Emerald Proto-Whelp both have that moveset combo. Sprite Darter and the emerald whelpling survive, onyxian whelpling is a goner. With so many beasts to kill, I'm saving my mechanicals for other fights. Onyxian whelpling can be subbed out for any dragon or pet with moves strong against magic.

Start with Sprite Darter. Moonlight, then Arcane Blast once or twice, then life swap. Switch to your middle pet until the pet dies, then back to Sprite Darter for more life swapping and moonlight. Finish off the extras with your emerald whelpling/proto-whelp.