GIF needed
A technique that has had an iron grip on the game for the last decade or so, ledgedashing lets you escape the ledge while invincible and actionable.
Failing a ledgedash will usually result in a self-destruct, and when it doesn't, will probably result in getting hit offstage by the opponent. Therefore, the consistency and quality of your ledgedashes are paramount.
Luckily, Fox is the best ledgedasher in the game. So good, in fact, that one of his bad ledgedashes may well have more invincibility than other characters' perfect ones.
You may have heard about the 16-frame and 15-frame ledgedashes and why they're not worth going for.