For me, I've always wanted to make WWE related MUGEN content. Namely characters and stages, but I could never find proper resources to do so. I actually wanted to base my entire creation/release process around Wrestling content.
Other characters I've always wanted to make:
Shoma (From Rival Schools Project Justice)
Natsu (From Rival Schools Project Justice)
Freeman (Garou: Mark Of The Wolves)
Vega (Claw Vega. From Capcom Vs. Snk 2)
Black Star (From Soul Eater.)
Stages I've wanted to make:
A stage based on the anime "Soul Eater". I've always wanted to do this.
A stage based on the anime "Samurai Champloo" as well.
As mentioned above, a WWE stage as well.