the Anubisath idol and arctic hair are tier 1 for the reasons I gave earlier.
The S/S death adder hatchling, for its ability to outspeed everything but critters and its blinding poison, and puncture wound combos.
The Unborn Val'kyr for its haunt ability, any pet with haunt is immediately tier 1 for its ability to treat the pet as dead, give a free switch, and for being the strongest dot in the game.
There's only 1 other pet with haunt, and thats the ghastly kid, who is also tier 1 for having the haunt ability.
The P/P emperor Crab, for being able to counter haunt 100% and for its overly inflated power value which allows it to hit harder, and heal for more than normal pets.
The S/S fiendish imp, for its ability to switch your opponents pet out before they can attack during the round, giving you a free turn, plus its immolation and humanoid racial combo very well to allow it to heal for a considerable amount in the back row while doing damage.
The Hydraling and Ore eater. Both are tier 1 for Being the only 2 pets in the game with the OP Shell Armor ability, a damage shield that reduces damage for a very considerable amount for 3 turns. The both also have a nice move set to go with their armor.
The Hyjal Wisp, one of the newest additions to the tier 1 list. This little bad boy is a fast pet with a dodge who also has the best heal in the game, wish. Making it particularly hard to kill
The Mechanical panderen Dragonling, for its decoy, thunderbolt, and breath ability, making it a double counter to magic type pets.
The son of sethe, the only pet in the game with 3 heals in all 3 slots, 2 of which are very significant, a high attack power value, and an undead type.
The H/H spirit Crab, this guy is probably one of the only undeads who can counter critters very easily. Its also got a ridiculously large health pool and can dish out a lot of damage. Also its undead, that undead racial is OP
The Teroclaw hatchling, one of the few flying type tier 1 pets. The teroclaw is the only flying type pet with a hot, who also happens to have a dodge. What makes this great is that flying type pets are the fastest pets in the game while above 50% health, which makes dodge 100 times better on a fast pet. Plus since it has a hot, you can always just switch the pet out with the hot active and bring it out later once its back above 50% health and has its racial active.
The Vengeful Porcupette, one of my favorite pets. This pet has a unique skill called spirit spikes, which reduces damage by almost as much as a shell armor for 1 round, and does a really nice amount of reflect damage. This ability is only really good if your faster than your opponent, which the porcupette can be if it powerballs a few times first, an ability that increases your speed by 20% for the rest of the match.
The Frostwolf Ghostpup, The hardest hitting ghostly bite user in the game, who also has haunting song, a team wide heal that lets you counter aoe teams pretty nicely.
The S/S Bronze Whelping, Has a controllable stun and a dodge in the form of lift off on a fast pet.
Weebomination, The only pet in the game with a spamable split aoe that doesn't lock you into the move, a super high health pool with a heal as good as wish, so tough to take out. Its also an undead. They should really do something about that racial.
The bone serpent, another undead. The only non flying type pet who can pull off the Darkness Nocturnal strike combo.
The fossilized hatchling and the Fragment of Anger. 2 more undeads. Both have very strong aoe abilies that dont rely on other pets to set up. The Hatchling is better though, since it also has a very nice heal.
Now I'm going to list all the tier 1 pets that are hard to get slash no longer available.
First off, we've got the murkalot. How I wish I had this pet. This the only pet in the game with the ability Righteous inspiration. Its a free switch ability that gives the pet who switches in double damage and speed for 1 turn. Combine this with a hard hitting aoe like the Fossilized hatchling or Fragment of anger to do just an absurd amount of damage to your opponents entire team.
Lil'ragnaros, a pet from the in game store, is the hardest hitting pet in the game, with an incredibly annoying trap and a submerge.
The Dread Hatchling, has the hardest hitting darkness nocturnal strike combo in the game. Although jungle beaks and crows can pull off the combo with pretty much the same effectiveness and are pretty good too. Its just dread hatchling is the best at it.
the Blossoming Ancient. Its just a really hard to kill pet
Graves. It has 2 really good Aoes on 2 separate tiers, is undead, has a lot of health and power, and thats just really good, kinda OP like the teroclaw hatchling and Shell sheild. Expect to see a lot of these pets in the near future.