Some doubts I have

Hey guys, i'm new in the forum so I apologize if this isn't the right section to ask. I've got myself an S4 recently and I've been watching videos but there is some stuff I still don't understand how to do. I'll share a couple of links so you can see what I mean and then ask some general questions that have been boggling my mind for a while:

http://youtu.be/0eeEIasIj4k?t=3m40s
In this video, when porter mixes from the Excision track to Slam the Door, can anyone help me understand how's he doing that mix? I'm trying to listen carefully but I don't understand what he does to pull that mix so nicely.

http://youtu.be/13jledvIfmI?t=7m25s
In this video, when he mixes from Unison (KP remix) to Windowlicker, all I can listen is that he drenches the whole mix in reverb, lets Unison's reverbed signal go for a couple of seconds and then he crossfades to Windowlicker, is this all he's doing or am I missing something?

http://www.youtube.com/watch?v=Aaq9_uqqQ-o
This one is just a curiosity thing only, how do you guys think they set up to play b2b as porter is playing from the S4 and skrillex is playing from the CDJ's, they just hook up the S4 to the pioneer and porter beatmatches by ear to the track playing from the cdj and uses the pioneer to mix? I'm wondering how they setup to play that way.

One last thing, any tips you guys have when mixing tracks that have really different bpm's, as this is being done by lots of djs nowadays im looking for some tricks you may have, i'm watching videos from guys (Nero, Porter, skrillex, etc.) going from dnb to a trap or moombah track and then to some electro-house 128 bpm track and they mix it so seamlessly I really cant listen in which part they're getting the mix/crossfade done.

Thanks in advance! Cheers!