Every MKX character has frames traps.
First thing that comes to me is his 1112 string.
Your opponent will never know when you'll end the string, which means you can do: 1, 11, 111, 1112 and add a smoke bomb after each 1... Do a throw after you stop... Poke, do another 1, or a low/overhead mixup...
b21 is that weird side switching string that can be ducked or armored out... You can just do the b2 into nothing if you want to mess up their inputs if they try to armor... Or do b2 spear... b2 EX spear... b2 EX smoke bomb... That's an idea of MKX frames traps... Basically, strings you stop to bait the opponent or to take another advantage...
Another example... You'll end in a restand, but you're sure your opponent will jump the smoke bomb if he blocks the overhead or low mix up, you can do b1 (or b3) and not do the smoke bomb afterwise and NJP to catch their jump out... (That's maybe too deep of a Yomi and I don't know if it's realistic and what will happen if they get hit by the mix up... And that defies the purpose of the restand... But well that came in my mind and I needed to get it out...)
I am sure people will explain this better than me...