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N.T.A.O ChangeOfHeart 死の剣
, it is useful depending on (I hate saying this, but it's true) how you use it. If you're float dashing around with no strategy or intentions, you're going to get hit. But because Peach can do any option if she is mobile with float dashes, you can use stronger, higher kill potential punishes, whereas you wouldn't normally. Players such as Kie and SlayerZ are able to fully utilize the technique in both their mind games and punishes. It's very useful because it opens up 4 fresh options and it gives Peach better kill potential because of how fast she can make the moves come out, and how strong they are.
A use of something similar would be her LIFT technique, where you are on the edge and still have your float, and you press + hold jump and hold down. You can continue with the float and punish an opponent that is recovering, or mix up Peach's recovery to the stage. You can also LIFT onto the stage and if you let go of down fast enough, you can power shield an MK's nado (and any other hitbox that is there at the time really) if done before your ledge invincibility runs out.