Nayeon - Cat Woman
Jeongyeon - No Face (Spirited Away)
Momo - Cruela De Vil
Sana - The Red Queen (Alice in Wonderland)
Mina - Mummy (2017)
Dahyun - Annabelle
Chaeyoung - Joker (Suicide Squad)
Tzuyu - Corpse Bride
source: Kurocam Channel, glintnayeon922, imbunnybong, brilliant_topaz, ringx3 1 2, twice_mm1020 1 2 3, wink_angel0201, roseofsharon324 1 2, dahyun_fan, tofulike07, honeychaeng 1 2 3 4, ddelta_trap
Jihyo's costume was...to say it mildly...in poor taste.
EDIT: This was debunked, she introduced herself as "Indian Jihyo" and even did a "war cry" (00:25s).
Whose costume did you like best Omona? I'm calling Chaeyoung Unni from now on.