Okay, so I caught an editor on TVTropes today mentioning a "BattleMaster IIC" in the context of MechWarrior 2. I, too, remembered the BattleMaster being labeled as such in that game. However, I can find no sources mentioning a "BattleMaster IIC" even as an apocryphal design, and I haven't seen a screenshot of the BattleMaster in that game's Instant Action during 'Mech selection in over 15 years at this point. I remember quite vividly that trying to pilot the thing would crash the game, but that's not what this is about.
Was it really labeled the "BattleMaster IIC" in that game? I know it only ever showed up in use by Kell Hounds in the campaign, so I'm pretty sure it was just a regular BattleMaster in context, despite using Clan-spec weapons and equipment because that's all that particular game had. It and the Tarantula (IIRC, the only quad 'Mech to ever appear in a MechWarrior title) were that game's only Inner Sphere 'Mechs, I believe...
EDIT: The BattleMaster was one of two (three, if you count the Elemental battle armor, and the other one was the Tarantula) 'Mechs that weren't normally available to the player in any mode. If you need to know how to access this 'Mech in Instant Action, you need to name your MechWarrior "Enzo". Though trying to actually deploy in it will crash the game; the AI MechWarriors can use it just fine, though.