Capturing fiends in Omega Ruins...

[Mjazi]

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?

[TheSpoonyBard]

Black Element. Two of them accompany a Spirit. Try looking down the left-hand path.

[Firo Volondé]

Also, Machea, which looks like the thing you fought at Baaj Temple when you first meet Rikku. It's found in the right-hand path of the fork you encounter after you go left from the entrance.

[Omni-Odin]

Speaking of this, it's so hard to find Master Couerls in this freakin place. I have more Master Tonberries than I do Couerls. Anyone know where to find more.