This could either fuel Metagross-GX itself or whatever Psychic- or Metal-type was used with it
If this card is Normal or Special Summoned: You can add 1 "HERO" monster from your GY to your hand during the End Phase of this turn
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
Temple Bell, Otherworldly Atlas, and Mikokoro, Center of the Sea are safer because you can time their activation to best suit your needs while still giving everyone the benefit of extra cards
Meanwhile, Elvish Archdruid is in our deck because it can potentially add absurd amounts of mana, which is helpful while we are drawing through our deck with Beast Whisperer
Getting these characters in play makes it difficult for opponents without the right cards to get rid of them, making it possible to rack up some lore without interruption
