Interestingly, the very first spell I thought up to turn into a creature was Magic 2010 )a 2U sorcery that drew two cards
A particular favourite of mine is Zendikar Rising, which took landfall cards and turned them into retro travel posters to reflect the planes intrinsic connection to the land and environment
Obviously, if a card says to flip a coin, you flip a coin, but otherwise, it just needs to be an agreed-upon process with an equal chance of getting each result
When the Ruby Moana quests at a location, you can ready all other players at the location (which recalls the Amber Moanas ability from The First Chapter )
This is a chaos engine in creature form
So, how do you handle 15 disparate characters who only share a name and (usually) some mechanical skill