Managed to hit 22 on my Clockwork Gnome, but I found a new favorite mechanical: the fireflux feline. It's the ideal glass cannon... I've never seen a pet that can hit so hard in a single hit. The trade-off is that it takes three turns to do so: Wind-up (10% damage boost) + Prowl (150% damage, -30% speed) + Wind-up (very strong ability) meant that below level 10 I was hitting for around 700 damage. At level 17, I would hit for around 1100. And you can repeat the process as often as you want, since none of the abilities have a cooldown (you can pick Supercharge over Prowl if you want to avoid the speed penalty, but that also gives a 3 round cooldown). Of course, this comes with a few trade-offs... Ideally you want a high-attack pet, but that nerfs your hp and speed. The fireflux feline also has no defensive abilities, which means you'll likely only get to use this combo twice before it bites it (including the mechanical death + resurrect). And of course it can be stopped with a number of abilities: fly/dive/burrow, for example... or cocoon... or evasion... pretty much any buff that allows a pet to avoid a single turn.
Then there's the issue of actually getting the pet, which took me a couple of hours. And the one I got, although green quality, isn't an attack-type... but still hits like a truck. I could solo a level 24 at level 17. Granted, I would die in the next round, but still... awesomesauce.
Edit: It's even more ridiculous if you fight a beast and crit. I think I hit around 1800 as my highest hit so far... and that was in the teens for pet level. Just dinged 20 on it.
Edited, Dec 10th 2012 8:09am by LockeColeMA