I've been using Chrominius the past two days for farming rare flying pets (while leveling someone else). Arcane Explosion does full damage to the front pet and half damage to the backline pets, no cooldown. His heal does have a cooldown. Since I was farming and not PVP-ing, I had Ravage in slot three. I'd spam Arcane Explosion until the flying pet was almost dead, hit Ravage, which would kill the bird and heal Chrominus. The likely critter backline pet would swap in at low health, and the second half of Ravage would kill *that* pet, healing Chrominius again. With Ravage on cooldown, hit Arcane Explosion (or the heal) again, then Ravage again. Since Chrominius is also a dragon, the second and third pets would usually swap in with Chrominius having the dragonkin racial up. The only times I had issues with this format was any dot heavy team, because my heals all came at once, at the end. A constant (or multiple constant) dot whittled him down a lot. Snakes teams were especially bad, for the dot and counterstrike.
I admit I haven't tried this in a few months, but when I was leveling my pets, I used a Molten Hatchling a lot. Leech Life in slot 1, Cauterize in slot 2, Magma Wave in slot three. Magma Wave hits the whole team with no reduction for backline like Arcane Explosion with no cooldown, and the other two slots are heals, although both have cooldowns. I'd take down whole teams with just the spider.