Okay, so there's a universal option select going around where if you cancel certain attacks into EX moves using 1+2+3 instead of button+block the EX move will come out on hit only. An explanation of the option select can be found here.
So how does this apply to Sub-Zero? I believe Alioune discovered this first but if you do Forward+4, 2 and cancel into down, back+1+2+3 you'll get EX Ice Burst on hit but on block you'll get Ice Clone. We should all know by now that Forward+4, 2 xx Ice Clone is unsafe on block with certain EX moves so be aware of that.
I haven't done any testing with the OS yet so I'm not sure what other normals or attack strings that it works with.