i used wario game 3 against fly amanita at ltc
http://www.youtube.com/watch?v=P--yhHbUCM8&t=9m25s
(Sound is horribly desynced, would suggest muting)
any critique welcome, especially from Luis
A lot of the trouble is that you were playing the matchup wrong. You tried to open him up via ground poking, which does not work reliably against Dedede. He has too many options that counter and out-damage you (CC leads to his enormous grab, tilts, shuffled F-Air, he outranges you safely, etc.), and Wario isn't fast enough on the ground to reliably give chase against Dedede there; it's relatively easy for him to go back to neutral position that way. You want to get him in the air so he has significantly fewer options.
Smart use of rising fullhop F-Air is your safest bet in neutral position, as Dedede's B-Air and F-Air are his best tools by far to deal with it. F-Air is intimidating but is slow to come out, while B-Air is fast but doesn't have much range, so good weaving through the air will allow you to find holes and combo, whereas Dedede only gets one or two hits when he gets a read there. Since F-Air sends him upward, you get more per hit, and you have to commit less. Use your ground game once you have him in a tech-chase position, but otherwise this is a match that will be won in the air.
N-Air's double-hit properties also help with crossing up, and his fatness makes him a prime target for Bite/grab stuff, which is great for catching his landings. Pressure his offstage game with N-Air, F-Air, and B-Air; Dedede is basically forced to swing with B-Air or F-Air and if he guesses incorrectly, he's probably dead.