As a mutating creature spell resolves, instead of entering the battlefield, it merges with its target into one creature
This works as a way to hide cards from hand disruption spells like Thoughtseize, as well as a way to accelerate your hand towards necessary threats and interaction
The iconic one is Kadena with a four-cost Sultai colored 3/3 that gives our first three-mana off
So if theres 100 Borderless Liliana of the Veil (only one special version), theres 50 each of Showcase Sheoldred and Phyrexian Sheoldred
Warhammer : Since they don't actually understand the sorcery they wield and can't decipher their own writing, in battle the Blue Scribes of Tzeentch sling spells at random without knowing what's going to happen
It's easy to justify mechanics with flavor, so in a vacuum, it's not hard for a card to just feel right