There has been some fan art but what if the idea was a manga short or a short anime like a one shot in a way if that's the case this is what would happen:
The lichs bomb turns others into the creatures and magic that's in the show and others have a different effect they turn into titans, the walls that protect everyone is the roots of the tree house that creates the 3 walls
Ice King/Reiner/ The Armored titan ( just with a shorter beard)
Lemon Grab/Bertolt/ The Colossal titan
Marceline/Ymir/ The Fast titan
Tree Trunks/Sasha/"Potato Girl"
Susan Strong (Thinner)/ Annie
If you have any other suggestions please comment I am a dummy!
Finns father injected him with the serum and he was sent to cosmic jail, finn gets eatin like eron and comes out a blone titan with blue eyes, finns mother is alive but then gets eatin like erons mother, finns weapons are two golden swords with mana roads, The military characters will be some banana guards, the citizens in wall maria are candy people and other creatures, instead of a king its a league of princesses, finn finds out that the lich is a fault for creating the titans but wonder who created the lich himself, the gumball guardians fight titans in the attack on trost.
If you any idea's you want to share please leave a comment