GMing 101, I learned this through experience - Mindcontrole is a no-go. Both for players (too powerful, busts plots left right and center), and for NPCs (players hate this like the plague, also, too powerful). Mindcontrole always needs very, very, super heavy balancing. It's super delicate. Usualy done by making it take a loong time (Ossy was with the knights for months, maybe years. totaly believable that they have been brainwashed to an extend that they would fight for him even if he turns into an ugly monster right in front of them), and if on friendly NPC good after a kidnapping, if done as a proper shocker. On PCs always after actually sitting aside with that player so he knows whats coming and can play along - which even further increases the shock moment when the actual player sais "I stab my friend in the back with glazed over eyes" than when the PC just tells the player "your character stabs the other character"
I can not stress enough how delicate mindcontrole is. Just a passive ability that happens to everyone around and doesn't even cost mana, and moreso, is just the icing on top of huge stats, powerful and plentiful underlings, the aria damage negation and who knows what else, that's overkill. That's not how you design battles
if the mind-controle is also inconsistent, it's just, yes, bullshit.
turn one, ICARUS is not éffected by the mindcontrole, scans and sees the demon
turn two, ICARUS appearantly now is effected, and attack the demon, and is stopped dead in her tracks by his sheer tankiness. She does not fly further and collapse the ceiling
turn 3, ICARUS still affected shoots her beam, the demon vanishes, and Ossy and all knights inexplicably collapse.
later Sanure claims the demon was never there - yet it very skillfully managed to block both icarus and her shot, two attacks that otherwise would have hit ossy, who between them time of icarus being not affected and affected, did not move.
when illusions suddenly start to actually act as shields, thats maximum nonsense. This is the very reason why I always lined up my attacks