The Ice Climbers' smash attack is brutal, especially when both of them hit someone at the same time. They can't always KO someone with one hit, but their smash attacks can do it alot more often than a lot of other people's smash attacks. Their smash attack is almost as good as Roy's.
On damage ratio 2.0 Dr. Mario's up+b upper cut thing is just as effective as a one hit kill attack as Roy's holding down b charging attack. Same with Falco's down+b attack. They also work just dandy on damage ratio 1.0, but damage ratio 2.0 is more fun so that's all that counts.
