Remixes
You can distribute a remix, but only if you have the right to use the original song. If it is your own song, you are free to remix it. If it is someone else's, you need permission from the rights holders before releasing. An official, cleared remix is fine. An unofficial remix of a track you do not control is not. See Distributing Cover Songs and Remixes through InterSpace.
DJ Mixes and Continuous Mixes
A DJ mix that blends multiple copyrighted tracks generally requires clearance for every track included, which is usually impractical for independent releases. You can distribute a continuous mix made entirely of music you own or have cleared. Mixes of other artists' commercial tracks will be flagged by content recognition and rejected.
Mash-Ups
A mash-up combines parts of two or more existing songs. Because it uses multiple copyrighted works, it needs clearance from all the rights holders involved. Without those clearances a mash-up cannot be distributed to stores.
Instrumental and Ambient Music
Original instrumental, ambient, lo-fi, and beat releases are fully supported, as long as the music is your own. Follow the standard metadata and artwork rules, and mark the release appropriately. Avoid misleading titles or artist names designed only to capture search traffic. See Unacceptable & Misleading Tracks.
The Golden Rule
You can release anything you own or have cleared. Anything built on other people's copyrighted recordings or compositions needs permission first, or it will be caught in Quality Control or taken down later.