Joeys right. I counted, and between the five games (Metal Mayhem, Advanced Destruction, Arenas Of Destruction and both versions of Extreme Destruction), theres only two that appeared in all of them. The total list...

FIVE
Chaos 2
Pussycat

FOUR
Panic Attack
Behemoth
Firestorm
Diotoir
Razer
Hypno-Disc

THREE
Wheely Big Cheese
Thermidor 2
Tornado
Dominator 2
101

TWO
Mortis
Stinger
Plunderbird 5
Terrorhurtz
Panzer MK4

ONE
Sir Chromalot
Milly Ann Bug
Purple Predator
X-Terminator
Dundee
Scutters Revenge
Terminal Ferocity
Crasha Gnasha
Onslaught
Cassius 2
Suicidal Tendencies
The Revolutionist
Bigger Brother
Rosie The Riveter 2
Tricerabot 3.0
Propellor Head
Destructive Criticism