Idol is a love/hate pet for most PVE battlers. It has a really strong and unique set of skills that make it perfect for carrying levelers against daily trainers, but its fights take a long time, and pre-6.0 it had a really high miss rate on attacks. If you want to level a carry pet against a trainer for 4000+ experience, you’ll very likely want to or have to use Idol. If you’re trying to speed level against regular 3-pet mobs you won’t want to use Idol. He takes far too long. The basic approach to a fight with Idol is to mitigate and dodge damage, use your humanoid racial bonus to heal over time, and chip away at your opponent. That means you have a lot of 20-30+ round fights.
Why is Idol so powerful? A very very large percentage of PVE world pets have movesets with a primary attack that ends up being a lot of little attacks that stack up to 250-400 damage per round. The flavor text will say something like “1-2 attacks for 110 damage, plus an extra attack if the user goes first.” More elite trainer type pets often hit you with a DoT type burn/bleed/poison attack too. Sandstorm and Stoneskin cut ~70 hp off of every one of those attacks including the DoT’s, which can completely negate all damage you take in a given round. Even against the MoP Daily Trainers, most of their critter and flying pets use attacks of those types. With Sandstorm up against many of the trainers you can run a very low level pet in (against some as low as lvl 1) and get them fight experience without taking damage or taking very little.
The other reason Idol is so powerful is he has a dodge skill that always goes first. Being a slow pet you very predictably tell when skills like Burrow and Lift-off are about to hit, and avoid them. So you’re mitigating the little attacks, and avoiding the big ones altogether. The trade-off is that you’re doing an average of 200 damage per round against a 3-pet team with 4500-5000hp.
Finally, Idol is one of the few humanoid pets with a viable moveset. (Bonkers is a good one too.) Since there are a lot of Dragonkin in the MoP daily trainer series who hit really hard, you almost have to put in a pet with a strong Humanoid attack to counter that. The Humanoid racial bonus is significant too. As an H/H Humanoid he will heal just shy of 70hp every round he lands an attack. That’s significant when you combine it with his other skills.
Cast sandstorm or stoneskin, crush, dodge, crush, crush, repeat.