I get a lot of questions from friends and other pet battlers on how to tackle this boss. So I made a little post here and on wowhead if anyone would like to see it.
Guaranteed win with 1 pet and 2 carry - long but easy method (2 carries are optional)
Pets: any pet that can survive 1 cast of rot, and pet that can take one tick of the swarm fly. (Normally I go with pets above lvl 9)<Puddle of Terror>
Slots: Carry 1, Carry 2, <Puddle of Terror>
Cycle through your 1st 2 carries, then with <Puddle of Terror>
open with <Sunlight>
Cast <Nature's Ward>
Keep recasting ONLY <Nature's Ward>
is up, then cast <Sunlight>
. Recasting Nature's Ward negates the effect of rot turning you into an undead so the Swarm of Flies dot will do very little
Repeat this process. I know it takes forever.. but the goal is to DPS the back-line enemy pets till they are dead or nearly dead with <Sunlight>
. Kill Idol with <Sunlight>
Finish off with <Punch>
if pets remain (should only be 1 cast, and mech passive should have already been spent)
Note: If it looks like Idol of Decay is about to die and Gyrexle has not spent his mech passive (never happened, but I guess you could get some really lucky sunlight crits on Idol), pass on the sunlight til Idol of Decay has rebirth has a 1 round cooldown, then kill him with sunlight, his passive and rebirth with proc, and you will have one more chance to cast sunlight before Idol dies. (He will cast it on CD when at low health)
Hope this helps with people with limited pet pools, or people trying for their Plushie achievement. I do it this way to level up some lowbie pets.