Viliains Z-A

V - Valigarmanda (Final Fantasy VI Advance)

Ultima (the spell from Final fantasy, not the game series)

T - Tiamat (one of the four main bosses from the first Final Fantasy)

S - Scarmiglione (Final Fantasy IV)

Rubicante (FFIV)

Funny that you mentioned one of the FFIV Archfiends. A F2P mobile game I'm currently playing had them as summonable characters you could have as allies. I got Scar and Cagnazzo, but Rubi and Barbariccia still elude me. Fortunetly they can be still summoned outside of the event so someday I'll get the 4 of them and have a party of them and Golbez for the lolz.

P - Pinky (one of the ghosts from Pac-Man)

Ouroborous - Bone dragon enemy from SotN

N - Neo Bahamut (Final Fantasy VII)

Mancubus - Doom II

L - Lizard King (Dragon's Lair)

K - Karnov (Bad Dudes)

Jenova Synthesis (Final Fantasy 7)

I - Intangir (Final Fantasy VI)

Hojo (FF7)

For a good laugh, look up Final Fantasy 7 Machinabridged by Team Four Star. Have fun with that.

G - Giga Gaia (Chrono Trigger)

F - Freddy Krueger (Nightmare on Elm St)

E - Eggman (from the recent Sonic games)

D - Demise (Skyward Sword)

Chaos ( Final Fantasy )

Barbatos (a end game boss in Dragon Quest IV on NES/DS and, in JP/EU PS2)

A - Asteroids (from the game of the same title)

Z - Zora (StarTropics)

Y - Yellow Slime (Final Fantasy IV)

X - Xanhast (Baldir's Gate Dark Alliance II)

W - Wario (from Super Mario Land 2; remember, he used to be a bad guy)

Vulture (Spider-Man)

U - Undead Knight (from Final Fantasy 3...the real 3, not the one that was actually 6)

T - Triclyde (Super Mario Bros 2 USA)

Sedusa (Powerpuff Girls)

R - Red (classic Pokemon Blue Version)