on picture a d3 game where the area is one giant graveyard. Skeletons, zombies, and graverobber humans can attach you, but when they all die, they combine into one boss character.
A throne room lined with statues on both sides of the wall, they could be any kind of creature, or character class, and build. after you pass the statues the come alive. All are immune to elemental damage.
A volcano, or lava land, within this area is nothing but lava and fire golems. You could do this for all elements too.
NPC characters of the player character classes and builds ..... HELL BONE NECRO ANYONE? lvl 99 Hammerdin, HEHE.
DRAGONS!!!!!!!!!!! one for each element.
Mirror characters, NPC of your character, all the same skills, same lvls, same stats ect.
Chimeras, Living trees (immune to all but fire), Necro summonners(immagine that in a group of 2 or more), OH MY!