Mutate turns two or more creature cards into one permanent, merging their abilities, and usually granting a special benefit when you do so - but the specific wording of the rules generates many edge cases you need to be aware of
Arguably the only strategy that works exclusively in multiplayer Rakdos decks is chaos
though they'll probably vary a good bit in terms of how complicated they'll be to pilot
We also needed something for chocobos to do, and the saddle mechanic didn't exist yet due to the development timelines of Outlaws of Thunder Junction and Aetherdrift
That means cutting cards that dont cleanly fit into either role, or which are redundant versions of effects we have already graveyard decks can easily access huge chunks of their library each game, so variety is more valuable than depth
He could even make a decent Commander, albeit one that limits you to a mono-white deck