Almost everyone knows how to do that though. So you can't blame him for assuming...
Dash in one direction, C-stick down, quickly smash Up-A & Z. You kinda need to hold you controller claw style to do this.
I like setting L to Attack. Run, C-stick Down Smash up + L.
EDIT: This is the mortar slide i'm not sure if Falco's **** is any different
You don't need to do any of those. In fact, that seems extremely unnecessary.
For the Dash Attack Canceled Up smash (Aka Mortar Slide): Dash -> Dash Attack (I use c-stick) -> Up+Z before the dash attack hit box comes out
This move simply gives you a running up smash with a huge boost in distance.
For the DLX (as dumb as that name is...) Dash -> Dash Attack and connect with it (I use A) -> Up smash immediately once your dash attack connects (I use c-stick).
This gives you two very fast moves, and at low-low mid percents, the second hit (the up smash) should always connect. It's a good way to add some damage in on characters that you can't chain grab, like Marth.
Also, there are a lot of threads for both of these techniques; in both character discussion, and tactical discussion. Proper searching would have circumvented the need for yet another duplicate topic.