I've been playing almost only Mega Man in the demo with some friends. I tested some stuff with one of them.
If the opponent spams jab after your 3 pellet jab/ftilt combo he'll punish you if you are too close, but thats not very often if you mix well your moves. Also, SH away when you finish your pellets (if you are not going for a running grab). That will give you an excellent position to catch your opponent's roll/pivot grab/approach/etc. After the SH backwards you can buffer another ftilt/FSmash/etc.
Top Spin (dash attack) have decent priority... Same as Mario's ftilt and fireballs and Link's arrows and boomerang. TS couldn't clank Link's tilts tho. Sometimes you can pass through Link's bombs without exploding them with TS.
TS deals days of hitstun, a lot more than dtilt.
Mega Upper have good priority, you can cancel proyectiles with it. Not sure but probably got some armor or invicibility frames because I could hit through a Villager's FSmash (I'll test more about that next time I see my friends).
You can pass under proyectiles with dtilt. Even under Pika's thundershock if you time it. Dtilt is amazing for edgeguarding (specially if you jab your opponent off stage).
Nair is really good to edguard off stage. If you hit Nair with the sweetspot (with the buster) the knockback is straight forward and your opponent wont be able to recover (unless the character have godlike recovery like villager). I think that Nair sweetspoted is way better than Fair off stage.
In one game, I stage spiked my friend that was recovering with Link from below the stage with my DSmash near the edge. We tried to do it again many times in our tests without success
You can run off the edge and immediately press back to grab the edge. Could be useful if you want to trump the opponent or if you want to get a good position to bair him/her.

Well, thats all I found in today's tests
