He is just a NPC that rolls some dices, it can be good for you or your opponent but if you attack him during PTS he will help your opponent and not you (for good freaking sake) don't do AoE of course he get pissed if you hit him.
Luck has a say to this, he sometimes help you or sometimes helps your opponent but it all comes from his dice rolling..
Help can be: DEF+, TP 100% MP gained and healing, this goes for both you, the opponent and your pet as fight.