Have it in a hole then when player arrives, it jumps out then attacks him...
then close shut all the exits/ entrances and make it into a mini 'boss' level.
Or maybe put a trap door on the level above then when player arrives, trapdoor opens then blahblahblah.
Or make doors around the room. Player enters, doors open (exit/entrance shuts)all the little saurs` come out to attack him.
[A]NJL`s [N]on-[G]oody-goody [E]xtermination [L]eague [C]arrying [O]ut [M]ass [M]urdering of [A]NJL`s [N]efarious [D]evotees -Essence of ANGEL COMMAND