As a Frost main, he did the worst MU for Frost. He missed a lot of opportunities to deal against Liu. Allow me to explain.
1) Right at the start of the match, he could do 13xxFreeze (Amp DB4), j.2, B32D1, 1, dash, 13xxDrill (BF4) for maximum midscreen combo damage, but instead he did the 134, which was the OH at her string. First mistake.
2) Instead of spamming BF3, he could spam DB2 for zoning, since this leads to the HKD. BF3 is just a kind of a restand (which similarly the DB4 has). Second mistake.
3) He could even go for D4xxDB2B for OKI setup to add more damage against them. This somehow prevents them from jumping at the right distance. They would have no other choice than to either risk their ass to charge in, or to block low. Third mistake.
4) At corner, he did j.4xxDrill. He didn't even do this: j.4, 13xxFreeze, j.4, 4xxDrill for a bit more damage. Same goes for the other corner carry combo that he could even do double B32D1. Fourth mistake.
5) For pressure, he never used the other strings. Only B22 and 13. The other strings are useless, because they're either high and fast, or mid and slow with huge gaps, except of 344, which is a good baiting one. He didn't even use B3, which is the only low starter for the string, and Ninja didn't know that. Fifth mistake.
6) He used too much that useless Ice Barrier (DD3), and it did cost him too much. He could even get close and jump a bit like a froggo. That Ice Barrier, that you guys saw, is slow AF and can be ridden with one projectile. If Amp, it's getting faster and further, but AGAIN be ridden with one projectile. Final mistake.
And for all those mistakes he did, he got DLed by Ninjakillah.
Frost is suffering from her strings having too many highs as string starters leading to mid, and then to either low or OH. What's worse, almost all of her slow strings, like B22 and B12, have HUGE AF gaps. And now, after seeing the match, I'll have to add to the list of useless specials her BF3, because it has a gap, but it's good for far AA.
This is why most have dropped her, thanks to NRS.