Ive not seen much talk about double counter pets, but I could be interested in seeing what people have found or use:
Undead takes less damage from dragons and only one Ive seen with humanoid attacks is Scourged Whelpling
Beasts takes less damage from humanoids, and out of the grubs with undead attacks Mr. Grubbs
seems to be the overall best one to milk the undead attack.
Aquatics takes less damage from undead, and from what Ive noticed frogs is those with critter attacks. But with tonguelash requiring high speed to work consistently, Leopard Tree Frog
seems the definite choice with its 325 speed.
Mechanicals take less damage from magic, and the only mech with dragonkin damage is Mechanical Pandaren Dragonling
Humanoids take less damage from critters, and while theres a few humanoids with beast attacks, I feel Curious Wolvar Pup
really stands out as a critter mauler.
Magic pets take less damage from aquatics, and only one with flying damage afaik is Jade Owl
Critters take less damage from elemental, and snails in particular have a nasty aquatic attack to hurt elementals. Like a breed 6 Shimmershell Snail
Mechs stand out as having a singular hard counter in elementals that both takes less damage from them as well hurting them with elemental attacks. I am fond of Elementium Geode
with its combo of crystal overload and stone rush.
Dragonkin takes less damage from flyers, and while there is a lot of dragons with magic attacks to hurt flyers. I find that Chrominius
stands out with his 1shotting potential from Howl+Surge of Power
Fliers take less damage from beasts, while they are hurt by mechanical attacks. Only pet with such a combo is unfortunately the Dragon Kite
tcg pet as far I know.
What other pets would you folks think of note for this list? Though I would say it makes a quite good core for any prospective pet battler looking to make solid teams.