2: swap back to nether faerie dragon
3: life exchange
7: swapt to nether faerie dragon
8: call darkness
9: nightmare (if the whelp dies the battle will most likely be a loss)
12: surge of power
Just did this with 3 Saurolisk Hatchlings (BfA vendor pets)
Just used Rend, Burrow and Feign Death, but I am sure someone skilled could find a use for Rampage on one of them.
Feign Death always goes first, like Deflection so you can avoid the Void Gates. Rend and burrow work well together as you can cast rend and then burrow and the speed buff falls off. Then you can be undergound for a flurry and a void gate.
Took quite a few tries, but the pets were easy to get. Had him to 1 hp once, and 200 ish quite a few times. Some of the fights went 35 rounds, so it's not easy to give a real strat.
Only strat that worked for me, cred to Istalri on Wowhead:
NOTE: As far as I can tell, there is no replacement for the Nightmare Whelp. This strat requires the stacking healing debuff making Round 11s heal always equal 0.
Nether Faerie Dragon H/P (Life Exchange)
Nightmare Whelpling H/P (Call Darkness, Nightmare)
Chrominius H/H (Bite, Howl, Surge of Power)
R1) Nether Faerie Dragon Pass*
R2) Nether Faerie Dragon Swap to
R3) Nether Faerie Dragon Life Exchange
R4) Nether Faerie Dragon Pass*
R5) Chrominus Bite
R6) Chrominus Howl
R7) Nether Faerie Dragon Swap to*
R8) Nightmare Whelpling Call Darkness
R9) Nightmare Whelpling Nightmare (If Whelp dies, battle will be a loss)
R10) Nightmare Whelpling Pass*
R11) Chrominus Howl
R12) Chrominus Surge of Power
The Infinite Hatchling has to die on Turn 3; if not just give up.
Yula has to be dropped to 117 health, so save Life Exchange if Snozz only hits her one time and Breath instead.
It really really helps if you can get a critical hit.
I didn't succeed before all these things happened. Perservere!