How is this chain grab being performed in this vid?

[sirmackerel]

http://www.youtube.com/watch?v=PHzSbzqczG0

He does it for the first time at around 0:10 and then again at around 0:22. Is it just a down throw followed by a dash grab over and over? If executed perfectly, is this inescapable until you reach an edge? Also, is it possible to consistently start this chain grab with Nana instead of Popo like how he does at around 0:10?

 

[Needle of Juntah]

id say yeah, i mean its right there in the vid.
IC's shouldent have came back i just realized why im not playing brawl for very long

 

[Paxz]

http://www.youtube.com/watch?v=PHzSbzqczG0

He does it for the first time at around 0:10 and then again at around 0:22. Is it just a down throw followed by a dash grab over and over? If executed perfectly, is this inescapable until you reach an edge? Also, is it possible to consistently start this chain grab with Nana instead of Popo like how he does at around 0:10?

The combo is done just as It looks, and yes you can start the combo with Nana and keep going.
You should check my matches http://smashboards.com/showthread.php?t=147862

 

[pixcalcis]

I also think you should check out his matches...and any other ones he has on youtube....his chain grabbing is superb

 

[Lightning Ice]

Unlike in melee you can control which direction she throws them, which makes this combo possible. You could abuse Nana's AI and do this near the edge in Melee because she always throws towards the ledge if it is near but it wasn't nearly as effective.