I've captured all of them except one. You have to pay about 1500 gil to fight it in the monster arena. Where is he located and how does he look like?

Fiends I've captured so far(from my memory):

Master Tonberry
Master Courl
Floating Death
Spirit
Great Marlboro
Hamil or Hamal or something don't remember
P-something, big fire ball.
Veruna
and a very quick fiend starting with Z.

Who am I missing and where is he located?