Gotem all from kitty corps, the FD one is sick isn't it?
And yea, I do use Up B OoS a pretty good amount, I haven't seen those vids in a while but I'm not sure why I didn't do it much. I tend to go for bair OoS a lot just because its a lot safer and still has great knockback. Fair is just fast as hell and very reliable.
MK Mu... Once you get a lead its pretty easy to maintain, the problem is that if you let MK get the lead first it skyrockets in his favor. From a neutral position he has much better options than us, so the only thing you can really do is bait and punish until you get a lead. The key is to try and not commit to any approaches. You can punish almost anything if he whiffs, so try to draw out those opportunities. The only time I'll commit to anything in this matchup that isn't a neutral is if I'm confident I know what he's going to do and am going for a hard read. Besides that its a pretty systematic matchup.
Once I have the lead I just camp the **** out of him, bait and punish nado, etc.