What i always use and is a great method to open up people is as follows.
my favorite string is 421 because
4 is +2f
4 2 is +2f
and
421 is +2f on block
4 has 10f startup and can be ducked. If your opponent blocks then it is your turn.
When i manage to hit the opponent on block with 421 i dont cancel it into anything( i mean why should i do something unsafe when i can keep my 2 plusframes.) i walk back or backdash so the opponent whiffs and can easily whiff punish and full combo ur opponent with b1 or even b32 its up to you. You can also just use 4 2 which has a decent pushback. So it means that you get to the right distance to make the opponent whiff something. If they cant deal with the pressure or dont know the match up they will run at you or do something that you can punish. If they jump then use rising karma into a combo(in balanced of course)
and push him full screen away to restart zoning again^^
another example.
Lets say you play against a kung jin player. Most of em will try to mash out his db3 ex. ull block or just jump back so u can punish. there are a lot of situations that you gain with 421. you can also use 441
to vary a little which is also +2f on block.
but be carefule using rising karma. Ur opponent can just cross you up so that you whiff and that is the least thing you want.
I hope i could help with that.
a little if someone doesnt agree please correct me
