Celerity is a level 5 air spell that improves the initiative of a champion by 1, and costs a whopping 250 mana. The killer feature of celerity is that it has no upkeep and can stack with itself. In theory. In practice, you can only cast it once per champion. I suspect the equivalent spells in other schools may be similarly broken, but have only tried celerity.

As a side note, the implementation is pretty questionable: It doesn't actually alter the champion's base stats, it just applies a permanent enchantment named celerity. That's not very exciting; all the other enchantments work that way. I would expect a spell this expensive, with a permanent no-upkeep effect, to work by directly altering the champion's base stats. This way, champion you're building isn't merely caked in enchantments when you stack magic like this -- they're molded by magic into something more than human.