I assume you mean N64 Trilogy's Sub-Zero which had all Sub-Zero's moves.

The answer is: he was the younger Sub-Zero. He had his story and I'm pretty sure he had his ending. The End.

He had younger Sub's bios but had that weird, ambigious ending that at the end of the day, becomes non-canon with the Noob Saibot plot.

Super Sub-Zero however is basically Classic Sub-Zero with all of younger Sub-Zero's special moves from MK2 and MK3 or you could call him the ambigious non-canon Sub-Zero with lots of deadly moves, but that's just my crazyness there for you.

Is this Super Sub Zero really deadly ?