I've been playing around with the Ice Climbers recently while trying to find characters who can use the footstool jump in order to combo, and I found something quite cool.
For starters, when you footstool jump someone close to the ground so they flop onto their backs, this can't be teched, leaving your opponent open. Footstool jumps can be performed on opponents who are in a getting hit animation.
So here's what you do: Have Popo grab the opponent and hold them until Nana has recoverd from her grab animation. Next, do a down throw or forward throw (I prefer the latter) and immediately hold forward on the control stick and hammer a jump button repeatedly.
if you did it correctly, Nana will bounce off the opponent just as the throw ends, causing them to fall flat on their faces. Immediately have Popo do a squall hammer and carry the opponent forwards with it.
By now, Nana will have joined you on the ground again. Just as squall hammer finishes, have Nana run up and grab the opponent. Popo is totally free now to charge up a smash or continue for a chain grab or whatever your icy cold heart desires.
I wish I had the equipment to record a video, because this is quite a stylish looking grab combo. But it's really not that hard to do at all. Try it in training mode at a slower speed to get the timing of it down.
Of course, it's possible that the opponent could DI out of the squall hammer, but it's a fairly difficult atack to DI out of and chances are you'll just have Nana grab them if they do get to use their shield at all.
EDIT:
This can lead into the ice block lock. If you start hammering the B button right after Nana's first footstool jump, then Popo will fire an ice block, followed by Nana falling, de-syncing and firing an ice block. Perfectly sets into the IBL, proving just how versatile this combo really is.
