Ive for a long time been considering Chrominius as one of the more powerful pets with a quite nasty two-punch in Howl+Surge of Power. Plus Chrominus have a considerable healthpool to allow him to take the hits in the two turns of recovery right after.
Howl+Surge of Power doing 1480 damage to nonvulnerable targets at the cost of 2 turns of free damage on him.
But recently I had a closer look at the Core Hound Pup, and after leveling up one to 25 to try it out, I feel my hunch was right about it. It also have a significant pool of hp, nearly as much as Chrominius. Far stronger and far less points wasted in speed. Comming with Howl and Burrow for a 3 turn setup including a round of evasion, clocking in at 1196 damage done for the combo. With far less damage taken compared to Chrominius. The minus however is the 80% accuracy on Burrow, unlike SoP's 100%.
But as Ive tried it out, the Corehound Pup will last a lot longer than Chrominius and can pull of its combo more often. Making it more suitable for a first or a second pet. Whereas Chrominus makes a far better third pet for a brutal finishing blow to decide a pet battle to lessen the impact of the forced downtime.
Howl is the strongest damage debuff out there, and the Core Hound Pup is the only pet packing it with Burrow.