I'm assuming it's because they can send Simoon back to the hand, use their effect again and get 3 monsters with less than 1600 ATK in their first turn.
Effect can only be used once/turn
you want see you later to either return blackwing monsters to your hand, either someone flipped them facedown, or you can summon, whirlwind, search, see you later (monster you just summoned), special the tuner/monster you need. it's pretty useful since blackwings can special summon themselves as long as you got 1 on the field
Anoymous
BlackwingPlayer
