IIRC Brian's IRL nickname was "Kaibutsu" (Monster) and Bakushin O thinks that's good enough for a Halloween costume lmao.
Her IRL Counterpart became afraid of his own shadow, so the trainer equip him with a shadow roll (the noseband thingy) so he can't see what's below him, He was later called “シャドーロールの怪物 (The Shadowroll Monster)”.
It's Trick or Meat!Bakushin O, who heard that "Halloween is a day when you dress up as a monster or a ghost".What do you think, Trainer?!