I imagine that you have more freedom to come up with whatever fighting style and Final Smash you want when the characters are less defined.
I could see Ice Climbers have a few different Final Smashes.
1)The cause the entire stage to be frozen in ice making everyone slip around during the fight, except for them, because they are immune with their ice skills and shoes.
2)A huge Ice Attack they both use together to freeze people that get caught in it for much longer. Allowing them to push the blocks around or carry them and throw you over the edge.
3)A reviving Final Smash allowing you to bring back your partner.
4) Condor Attack is doable.
5)Blizzard attack.
6)They transform into Giga-Ice Climbers the two big bad muther-Ice Climbers.