Didn't have blightbreath at 25 used Naxxy as middle pet with 1, 1, 1. Dead Deckhand Leonard didnt use sweep with Frostwolf so was able to survive til corrupted slime used refuge and 1 scratch then died, then used Naxxy started with sticky web then leech then used plague breath with sticky web and leech on cd use your best judgement here I didn't have to use scourged whelping
This team as a whole still worked with an HS blightbreath, but I used bash instead and just had to go on the fly. Used bash when Blightbreath got pulled in, then swapped in my whelp as slime swapped in.
Sweep from Dead Deckhand Leonard is random. He seems to cast it very rarely, so it's unlikely that he'll force the pet swap on turn 3 as outlined above. In fact, it would probably be better to plan on him not casting it.
My suggestion is:
Start with Frostwolf Ghostpup
2+: Scratch until Frostwolf Ghostpup dies (you kill Dread Deckhand Leonard and 1/3ish of Corrupted Slime)
3: Ghostly Bite (during Frostwolf's undead round)
Bring in Scourged Whelpling
1+: Tail Sweep until you win. Bring in 3rd pet if necessary to clean up. Scourged Whelpling survived until the end on all my attempts.