pandaren monk it can focus chi and damage double damage.
sprite darter hatchling it have very very good attacks.
ghostly skull it can kill him self when he have died and healed again so the evil team get 50% more damage taken.
i use a maggot, shadeling and fire beetle, the damage is not amazing from them but all 3 of those pets have really good self healing which means against random critter fights i usually end on nearly 100% health. the other problem is none of those pets have good speed, but the maggot can increase speed by 100% for a few rounds. my team is not very good in pvp battles though, beast and critter are very common types and nearly everyone has someone to counter them.