Here are some more house rules for situations that will rarely come up, but will eventually happen at some point in the battle. I'll post them here first in case there are questions/objections, then post them in the rules thread later.
Dispel Magic: When dispel magic or greater dispel magic is used to target a spell, the caster must identify the spell exactly, through prior knowledge (his own spell or intimate knowledge of the spell caster) or a spellcraft check. For example, just because someone's buddy looks confused, he can't cast dispel magic specifically to get rid of the confusion and automatically keep all the rest of the buddy's buff spells intact. He can still cast dispel magic at a creature or object, an area, or as a counterspell without this restriction. Other spells like break enchantment or dispel evil also do not have this restriction.
Calling Creatures: Spells such as gate or planar ally that can call creatures to the arena that are not on a list (like the summoning spells) are subject to the knowledge restrictions specified for alter self/polymorph/shapechange. No creatures above CR 20 can be called into the arena.