Even more important, is there a sure way to find out who has it, and other ways it can be exploited now.
I was just messing around with UMK3 and I decided to see if there was a correlation between overlapping sprites and frame advantage/glitch canceling, because I always suspected there was and couldn't remember if we ever discussed it, but it's one of those things I never really decided to test. So anyway I was practicing some juggles earlier and I said "I really need to just test this out" hit F3, chose Reptile and Scorpion. Paused the game, held HP on both sides, frame advanced until contact and P2 Scorpion won. He also was beneath Reptile's sprite the frame before Reptile sold the hit.
Reset, selected the same characters. Pushed them up to each other, Scorpion was overlapping Reptile. Did the HP test. Reptile won.
Tested it again, predicted the outcome 10 times in a row. So I can say with much certainty that the default underlapping character has frame advantage, and the overlapping character can glitch cancel, but this could just be a major coincidence.
Now, I say default because there are things that cause the overlap to switch, but the underlapping character at the start of the round has frame advantage. If two characters go to attack each other at the same time, the advantaged character will win and always be beneath the other character's sprite, however, if that character does an attack, without resistance our non-neutral state, the advantaged character will then overlap until the other character attacks. This can be puzzling if you're for some reason looking to see if you have frame advantage.
It's still tricky, but this definitely is a surefire way to know, even though it has its own nuances and the window to see it is miniscule. If anyone wants to test a bunch of scenarios and lay them out, please do so, I have to leave for now and probably won't get back to this for weeks. Essentially, I'd like to know what moves cause the switch in overlap and the best times to notice it, other than the old simultaneous contact.