I add covers from YouTube mainly (most of my 300 added releases) and often artists just use instrumental of someone else and don't write a new one. Now I started to try to manage it with "uses instrumental of someone else/recording" tag, but it is too wasteful way and it is easy to forget it. In addition it is not systematical.

"mashup" is not useful and "remix" too, because they have different sense. 

Other example. Here is a playlist with covers of one song, and great part of them just use instrumental of original song: https://www.youtube.com/playlist?list=PLYnOd_hGdb-g7IcMYzUnacNddDZGeuYBH

Forward link phrase: uses recording 'x'

Reverse link phrase: is used in recording 'x'

Draft commentary: "This links two recordings, the first of which uses the other. For example, a musical cover where the artist uses an existing instrumental/arrangement and don't write a new one."