Fungus is like desiccating the kingdom and depriving it of its resources. The city is in a bad way because they don't have food and water because of the fungus but it's just because the fungus is like blocking everything. D evolution is also a room with a chair and you can put things into the chair and evolve them or D evolve them as you see fit. Koopa likes to dole out punishments that he will like like he takes toad who's this weird like Antifa troubadour and he D evolves him into a goomba.