Disable is a punish option. It comes out frame fifteen and can be jump cancelled, thus, allowing it to be used OoS. (5-6 frames faster)
It is also a read option. If you notice the opponent likes to do a grounded approach it is quite useful.
Mew squared uses it occasionally, pretty much the amount it should be used. At a high level no one is going to release something that punishable often, thus it is best used as a link/read.
Chances are that the opponent won't remember disable and will fall straight into it.
It is also a mix-up option. If you run into the same scenario three times during a match and you go for a grab each time, a competent opponent will realize this and react with a spot dodge. You can mix him up and go for the disable.
Also, disable can stun a persons feet. SH disable will stun people on the above platform, it might even shieldpoke. You can also just use SH disable to give it more length.
Dtilt-DJ Uair-Fair/Uair/Bair is a true combo at different Percents. I have it in the combo thread with the actual percent window.
The Jab on the Utilt-Usmash combo isn't true. It will never count on the counter. Only the Utilt-Usmash is. However, you can't escape the Jab-Utilt. Frame 2or something.
Dtilt-Fair-Fair-Fair is a true combo, I have done it and practiced it. Dtilt-Fair-Fair- DJ Fair. this combo works to some degree on fast fallers. Mainly Fox, it is very situational thus I didn't test it on CF.
FF Uair trues into many things, including Uair, jab, Usmash, Ftilt, Dtilt, Utilt, Bair, Fair. Their are multiple hitboxes and you have to hit with a certain one.
Meleebrawler, can tell you about these. Metalex can tell you about these. Raykz made a freaking video showcasing it. Maybe you should check the combo thread
Furret24
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Edit:
Smashifer
did you see the combo video of Nairo's Mewtwo? It shows one of the combos there. Also, it is in the combo thread, read through it as there are many combos and theories in there.