I am currently developing a platformer game (based on the recommendations of every person ever) and I am discovering that as I try to piece together the character, her abilities, the look and feel of the world and now the enemies, that I keep having really rubbish ideas. I don’t realize that they’re terrible at first, but then I come back to them after a trip to the bathroom and take another look… or maybe I show my wife the game and she makes a comment… and I realize that the idea I had is awful. It’s like, the theme of a stage is essentially “dessert”. And I have an idea for an enemy… a mushroom where the mushroom cap is a sombrero. And I tell my wife about it, and she is like… what does that have to do with cake? And I realize, oh shoot. It doesn’t. That’s really dumb. So I’m going to make it a cute, walking chocolate chip cookie instead. But the point is, I find I have to go through so many bad ideas just to get to each decent one.
Good ideas aren’t so easy. Great ideas even less so. Iterating helps and brainstorming ditching 9 out of 10 is a pretty effective way to go.
I find the more clear something is to me such as the story, the game play and so forth the easier it becomes to get better ideas. I make a simple story and that kind of guides the design of a lot of things. Basically I try to think of things that strengthen and support that story. Even if there never is a story actually told to the player in text or cinemas there is a story told by the location, objects, enemies, goals and so forth.
Also it’s often easier to come up with better ideas for someone else’s game. So I try to sort of pretend that I am actually looking at things that someone else gave me asking for feedback. That helps.
With your mushroom enemy there is probably a reason your mind went there. Maybe you are not clear on what you want to build? Or maybe you just thought a level of mushrooms would be cool. If so just file it away for a forest level or whatever. Creativity often works by just serving up all kinds of different ideas that might not be what you want at this moment but may be awesome for another level or another game. And maybe the mushroom enemy is fine. I suppose such a mushroom could have brainwashed all of the goodies and turned them bad?
Good luck!
The mushroom I think is because I keep drawing parallels between this game and Super Mario. In fact, I started out with Super Mario as reference graphics to kind of get the ideas going. But it is gradually becoming its own thing. Like right now, I have two interesting character abilities that I have never really seen done justice in any games. And I found out by accident that you can do both of them at the same time for great effect. Just the way the code worked out. So, gradually I think I’ll stop seeing mushrooms and koopas and start seeing this world.
It also sounds to me like you need to involve your wife earlier in the design process.
Having somebody to kick ideas around with is really helpful, and if presented properly, it might be a lot of fun for you both.
I’m currently making a platformer too, I can completely relate with what you are saying!
When I first started out, I had an Idea of what I wanted the game to be, but when I actually started writing and fleshing out my ideas, nothing seemed to work. The level designs, the story, the characters and even the enemies. Nothing seemed to fit together with my overall vision of the game. I was lost and mann I wish I could show you the amount of ripped pages from my notepad 
But after a bit of feedback from the people around me, followed by a lot of prototyping and of course a bit of rest to reduce the frustration levels, I was finally able to make things mesh!
Generally I write down all my ideas down whether they are good or bad (I try not to think so hard about it) because when I read through dev blogs, a lot of them say that bad ideas with a bit of tweaking can often be turned into good ones or recycled into something more interesting that can then enrich the game…
For the ideas I think are good, I try to just have faith in them till it’s proven they can’t work*…*But even then I just usually shelf them haha
Edit: I meant tweaking 
It’s stunning how much one incorrect letter completely changes the implied meaning of this statement!
Bad ideas are the stepping stones to good ideas.
@GarBenjamin is absolutely right. I would never completely through away a bad idea. a lot of times those are what led you to what is working. and might very well be the inspiration for many more good ideas.
I’m going to start implementing twerking into my standard dev practices right now.
If you live stream on twitch - I’ll not watch but up vote your post about it!
You could name him Zippy as a reference to the movie Nothing to Lose. (if you haven’t seen that, it’s a must watch IMO)
Zachary: Zippy!
Nick Beam: What is Zippy?
Zachary: He’s a cookie man.
Nick Beam: He’s a cookie man? What is that on the ground behind him?
Zachary: Oh, that’s a trail of chocolate chips. See, wherever Zippy goes, he leaves this magical trail of chocolate for all the boys and girls to…
Nick Beam: Magical? It looks like poop. It looks like piles of poop. It looks like Zippy is walking around just… Just crapping all over the place. It looks like…
Zachary: Those are chocolate chips.
Nick Beam: And what do you think it looks like? Zach, let’s say you are about to take a bite out of a juicy chocolate chip cookie. What is the last image you want floating through your head?
Zachary: Excrement?
Nick Beam: Excrement, right. Listen, I’m gonna go out on a limb here, maybe we should avoid all bowel related items on this particular project. Just a hunch, huh?
Actually I like the chocolate chip poop idea… that was already going in…
My my… How fancy
Most developers have wonderful ideas that turn out to be limited or broken when actually tried out because experience. You really do need to kiss a lot of Master Frogs to find your prince.
*Quality European Chocolate Poop
yes idea is all what you need. there is is over 7 bilion people with ideas:) good luck