Sub's 3 (even though horribly un-safe off-line) is a very good move online.It leads to a free throw and it hits mid.You can also do 3,2 (mid,high) and it will also give a free throw.You can also do 1,1,3, (high,high,mid) for punishing other moves since it starts out with a quick jab.This also gives a free throw leading to about 33% of damage.As you can see,Sub has easy and consistent pokes that lead into constant free throws and very nice damage.In addition,Sub is also a nice turtler.The Ice Clone is a good move but it has its delay now in MK:A;meaning that you can't do another Clone any more immediately after the initial one disappears.This does hurt his turtling and running game.
I won't go into any more details.He's just a solid and versatile character.He does lack aerial cancels,though,that keeps his damage under 40% accordingly.And off-line,he's very un-safe.
Tanya has first stance d+4.The best low in the entire game.It goes under high attacks because of its crouching animation and sets up 50/50 mix ups thereafter because it gives tremendous advantage on hit.Her aerial fireball gives free throws or 50/50 mix ups up close,and because Tanya is in the air doing it,it will naturally punish low attacks and other moves that have poor ranges as they will simply miss.She also has aerial cancels for huge combos as well as the non-damage reduction in her weapon stance combos as Konqrr mentioned in his post.
As for her weaknesses,she lacks decent mid attacks.Everything she has is usually punishable or parriable inbetween her dial-a-combos.She also doesn't track that well aside from d+4 and her throw.Her aerial fireball,although being very good as I said,puts Tanya at a disadvantage when her opponent blocks it up close or side steps it.Off-line characters can even catch her in the air (aa) while she's landing and then punish her which increases their damage potential.Thus,the aerial fireball is only good against some characters,such as Dairou.
Frost is just bad.Very poor character.She doesn't have one single mid move as unbelievable as it may sound.She does have 2,2 (high,mid),though,but that's it.All you have to do against her is watch out for the unblockable Ice Puddle.Everything else she does is duckable and punishable.In other words,when she misses her attacks (which are all high attacks),get up from the crouching position immediately and punish her (either be throwing her,uppercuting her,etc.).