Different schools really was my thought on it. Also the make them as differently as possible part was a suggestion and not an actual rule we implemented. I went with Dark, Holy, and War. I did a Skeleton Necromancer, a battle Priest with lots of help, and a Super Dwarf with only two other creatures for example. It was a friendly tournament at a local comic book store, not a major event at a large convention. Prize was store credit and an ice cream.