I made an account just to tell you this.
It's really hard to pull off combos with classic sub zero.
For example, I can't pull off these combo:
HP, HP, LK, B + HK, F + LK (26%)LK, B + HK, F + LK (19%)HP, HP, D + LP, D + HP (22%)
These are the official UMK3 combos for classic sub zero. (you may already know).
Sometimes it works the first time I try it, but the times after that, the hits just don't connect. Try it out, you'll see what I mean.