Coming from a SF background i'm used to anti-airing the living shit out of people with fast anti-air normals or fast invincible attacks. In MKX i now play as Sub-Zero again like i did in MK9. I'm having immense trouble trying to anti-air in this game, atleast with Sub-Zero. His D+2 just plain SUCKS this combined with how good a lot of jumping attacks are make it way too risky to even try it. Others have mentioned it needs to be done from a crouching position, i guess because of the smaller hurtbox initially. In short i'll probably won't even bother using this move when someone jumps as it gets stuffed constantly on startup. I would have to be extremely on point if i want to AA with this. Spacing also plays a large part it seems, further away the easier it is.
DB+1(Enhanced) seems a more reliable option however it is still not nearly as satisfactory, it is really really slow, 14 frames startupand unsafe on block so i'm gambling on the fact that people are commiting to a string after the initial jumpin and the DB+1 catches that....which everyone does, for now. It does give a free juggle though which is nice but it costs meter. Not an option to use everytime someone jumps it seems.
D+4 has the same startup as his D+2 but this move makes his hurtbox so low it low profiles a lot of jumping attacks, except attacks with large hitboxes and downward angled attacks such as a lot of jumping 3 or 4 attacks. On hit it gives very nice + frames which allow you to press your offense or atleast get some breathing room. It also works often against crossup attempts. This seems like a more reliable option to me and Tom also does it constantly. He also does run into f42 afterwards which can't be interrupted.
Another option which i find pretty good is his Jump+3, it is 5 frames on startup and has a nice hitbox it seems and it is active for 13 frames, so no timing required. Doing it from a backward jump seems the safest way.
*Quick question, why is it sometimes when i try to do a jumping attack as fast as posible it won't come out? Does it have a large amound of grounded frames before the jump is initiated, and thus it doesn't accept the input? I actually have to wait slightly before pressing the button, extremely annoying.
Backdashing from a jump or crossup attempt is pretty legit, initial invincibility gets you out of the situation reliably. Pretty safe. Some strings will reach if they've inputted it though and then they're right back in your face, overall i like this option though.
I guess you can also do an X-Ray, it has armour and it's safe on block and it freezes opponent when holding it...
D+2 imho is the absolute worst option to use against jump attacks, it's atrocious. D+4 and neutral/backwards jump+3 seem to be the best options.
This is just from my experience of the short time playing this game and i'm still atrocious at it but slowly i'm trying to learn it.
Good spacing and usage of the clone makes jumping a lot more difficult for the opponent but i'm still getting used to the game...hopefully it'll click soon.