User blog comment:Woest/Element consumption by Slayers/@comment-24934658-20140726121409

The 'slayer' cannot eat any Magic they produce meaning any Magic even if not of slayer origin could not be consumed by the slayer.

Benefits of fighting another mage is that the Etherion level is restored so basically its like a MP restore for the slayer.

Therefore Gray cannot eat his own ice creations but can consume the ice-makes made by Lyon which could or could not aid him in a battle against Lyon. Though if they fought Lyon would lose if Demon Ice Slayer is a permanent thing. Lyon could learn Ice Demon Slayer Magic there's no stopping him. Tag-team could go either way, its based on the situation one is in for one to be decided as eater and feeder.