Sprouts is an elemental. Prince Charming is aquatic. Runts is a beast.
These pets are pretty easy to beat with the right match ups. I used Garden Frog against Sprouts, alternating between Frog Kiss and Healing Wave on cooldown. I used Blue Dragonhawk Hatchling against Prince Charming, just repeating Quills over and over. Finally, against Runts, I used the Clockwork Gnome.