My findings:
1. You must have a free slot in your Pet list. Not the ones that says "Lv.require:xx".
2. Getting the enemy low in HP helps at least 20% or less (just like in RO!)
Of course you're more than welcome to comment/correct me. I'm not a professional and I just thought that someone else may find this useful since there aren't any guides yet out there.
Edited by althealice, 13 August 2011 - 05:08 PM.