The way Igursus' mirror mirror works is strange, when he gets possessed he reflects all on his own team, not on the enemy that attacked him, i understand he's possessed but shouldn't he reflect that to whoever is attacking him? Even a single target possession is reflected on himself.
This is based on the order of attack and reflection. I believe this is how it works:
He gets hit, the status effect (possession) applies on him first. Now his skill reflection kicks in, under possession, reflect to his own team.