Wrest Mastery takes up all ability slots, you can't have Wrest Mastery+RC+AI. Wrest Mastery teaches Disarm and Paralyzing Blow, as well as allows the pet to use Rampage (increases HPR/SR/SSI with each successive hit, until it misses) and Fists of Fury (attempts to land 3 hits in one attack). Wrest Mastery also causes it's regular auto attacks to have a chance of dealing much higher damage (like twice as much sometimes). Fists of Fury use is fairly random. My Wrest Mastery Fire Beetle never runs low on Mana from what i've seen.
My Wrest Mastery Fire Beetle outperforms my Chiv+AI 100% Fire Crimson Drake in Bedlam. The only thing in Bedlam that it doesn't kill fast is Red Death (which has 90% Fire Resist), which is why i avoid pulling it when farming keys for Monstrous Interred Grizzle.