Yes, you can release a mash-up through Too Lost, but only if you have the proper documentation.
A mash-up is a creative work made by blending two or more pre-recorded songs, often by overlaying the vocal track of one song onto the instrumental track of another. Because a mash-up is considered a derivative work, you cannot distribute it through Too Lost without permission from the copyright holders of all the original songs used.
Please note that a standard cover song license does not grant the rights needed to release a mash-up through Too Lost. For more information about derivative works, please see our Help Center article here: What is a Derivative Work?