If you grab any character near the edge of the stage (facing the edge), Nana, if she grabs, will always F-throw. With that in mind, Azn_Lep told me this:
grab, P-pummel + N-blizzard, D-throw, Nana regrab, P-grab, P-pummel + N-blizzard, D-throw + N-U-smash.
This will 0-death Puff, and with a bit of damage on before, or more pummels/f-tilts, can 0-death any floaty character. The Nana regrab is a bit tricky, but very useful. Just grab with Nana just after the enemy is bouncing up from the floor out of Popo's D-throw. Remember her six delay frames.
If you aren't near the edge, you can still use blizzards, pummels, tilts, Nana regrabs and Smashes to rack up an easy 40+% percent with a grab. And ending with U-smash or D-throw leads into Uair to Bair. So that gives you an offstage floaty with at least 60-70%. You can also attempt Nana regrabs anywhere, because if she F or D-throws, you can P-regrab.
Ice Climbers ****.