Ah Jesus, just tried him for 10 mins there & loved it! I asked for the MK9 Reptile & I got close, wish I could do the NJP after the 421 tho
i still can´t do it consistently aswell :/
One tip is to hold up and slide you thumb over 2-1 after the dash. I know, this is well known from mk9 days, but there is an additional trick:
If you slide the thumb through 2-1, and always be sure to make mistakes on the side of anticipating it, sometimes you'll get the njp correctly and sometimes you will input it too early and the string 21 will come out after the dash. Either case you get a combo. If you see njp hitting, follow up with 21, f412~ender. If you see that 21 came out instead, just do f412~ender. It's pretty much simple to react to.
This way, even when you fail, you succeed
Just make sure you don't press 2-1 too late. It's the only of the 3 scenarios you'll drop the combo. And, of course, if you slide the thumb from 1-2 it doesn't work also. It has to be from 2-1 and inputing it on time or early.