I hate that grab- but it doesn't belong in the ban column. Metaknight should sooner be banned from tournaments than the Ice Climber's chain grab. It doesn't make sense! Hylian brought up great points at the beginning of the topic, but I thought of some of my own on things that can prevent this.
1. Tripping- Both Popo and Nana are succeptible to this, giving you twice the chance to trip, only one of them has to trip to mess this up. This isn't majorly likely to happen but it could.
2. Nana is dead/separated- yes this happens quite often as Nana is a much easier target than Popo. Characters with great range like Marth can really knock Nana out quickly and change the game around.
3. Counterpick stages with different heights/obstacles. Obviously this grab works great at Smashville, Battlefield, and FD. But what about Lylat, Castle Siege, Norfair, Brinstar, Halberd, Delfino, Hanenbow, Pokemon Stadium 1, Pokemon Stadium 2? That is more than enough stages to mess them up. They can perform it for a little while at a few of these stages, but it will be difficult.
4. Ice Climbers error- This is a high error ratio effort! People wil not do this perfectly everytime, there will be a mess up. Especially under pressure.
5. Don't get grabbed- people know well enough that the Ice Climbers grab is dangerous and keep their distance and using characters and stages that are great for spacing against the IC. People will expect the grab, and IC will not get to use it every 10 seconds if the player has half a brain and some kind of talent.
If you ban this, you need to also ban:
-Dedede chain grab
-Falco chain grab
-any stage that has a wall or can have a wall (pictochat, rainbow cruise, corneria, pokemon stadium 1)
-any stage that doesn't have pitfalls (mario circuit, green hill zone, Onett, yoshi's Island (melee), Castle Siege)
-Metaknight altogether
My $0.02