It would be pretty awesome if Sub had a chargeable ice ball with 2 levels of charge. Without it being too crazy...
DF2 would give us exactly what we have now (charge 1) which scales poorly as it does now, but is slightly faster on start up like Cryo's hammer, comboing normally off of 11, in addition to new b33 and 12 links (again, similarly to what Cryo's hammer does). This charge 1 ice ball will be as punishable as current ice ball is on block. But executing DF2~2 gives a level 2 (charge 2) which scales ~2-3% better, moves across the screen faster, builds meter equal to throwing two ice balls, and only combos off strings/ normals with higher cancel advantage such as b12, f4, and 111 for Cryo (but able to combo normally in the corner off 11, b33, 12, etc.). Charge 2 differing from ex ice blast in that it doesn't eat other projectiles, is still a high, has much more recovery (making GM whiff clone > jip a tight link), and start up is longer creating a large gap if the opponent blocks the string preceding it (with the exception of f4, as it's SZ's jailing normal).
Make charge 2 dash/ run cancelable for 1/3 stamina in Cryo , make both charge 1 and 2 eat/ break opponents projectiles for Unbreakable so he can zone or turtle successfully as a defensive variation, and leave GM the way it is. Aesthetically, make it look similar to ex ice blast and provide an audio cue when it's casted successfully.