Simple rules, you pick a Mugen character for the post, any that you want, and you defeat the character from the post above using whatever power, either something you want to make up, or from the actual move list of that character.
And yes, you can use characters that were beat previously. It's all about spam and fun
I am the Carnage Cosmic and I just sucked Captain America into a Micro Black Hole.
So now, someone picks whoever to defeat the Carnage Cosmic however.