okay well my plan is to have 4 areas of the level, and each of then being seperated by camps, which are smaller areas, with a boss area at the end.
the first area is just a stretch of land with trees and a few necropolises ( those pyrimid things in the design
the first camp sets up the story, and is the human camp.
the second area is the slopes of hyjal. this area will have the most mario enemies.
the second camp is legions out post in azeroth and there will be a mario mini boss, i'm thinking one of those giant boos as they are undead.
the third area is mainly cliffs that you have to jump up using sonic springs/ musical note boxes. it contains the most undead, so it will have the reguler azeroth undead, plus skelton koopas and a few flood.
the third camp is where the mini boss with arthas is located.
the fourth area is the roots of the world tree, crawling with demons. but to help you are night elf npcs. at the end of this area you get teleported to the top of the world tree to face archimonde.
the boss area is the world tree yggdrisal which will be a a large area, where you fight archimonde in some epic boss battle.
whaddya think.