Merman Cabin In The Woods. The merman is one of the monsters kept in the facility. He was released during the system purge but is only seen at the end of the sequence.

Hadley (bradley whitford) finally gets to see a merman as other monsters wreak havoc on the facility. He was released during the system purge but is only seen at the end of the sequence. He is listed on the whiteboard and is bet on by steve hadley, as he has never seen the merman before.