Apologies, didn't mean to sound like that.
But if you're above them, they should know what you're going for, which is an aerial approach. And while it's the worst idea ever, there's really little room for imagination, there's nothing else you can do. Any player can just wait and sit in their shield and punish whatever you land with. If they decide charge a smash attack, then yes, you can punish them, but that's their fault for committing to a terrible option in the first place. Whatever Dedede does in the air is super easy to react to because of his awful air speed.
Generally if you're waiting above them, they can very easily punish you with aerials, as your options in air combat as Dedede are extremely weak.