different types of bolt for the crossbow (similar for arrows for a bow),
a better grip for swords,
new axe heads to do different damage,
or enchantments that target only equipment,

you can make Arrows/bolts, javelins, Spears, throwing weapons have the spellbind trait. attach the damage spell to them. So when they are thrown, either hit or miss if missing is possible, that weapon/projectile is placed in the area, and would have to be retrieved to be used again. It would also be possible for the other mage to pick up said item.

Spell Carrier items like a balloon, floating ball,or shadow clone/creature (movable traps) that wind or push spells can move them from zone to zone until the trigger causes them to activate.

Gravity spells that cause things to be immovable or reduced gravity where the space dosn't take a move action, you are so light it is effortless to move across the space.

Slimes and jellies that move slowly around the map eating spells/zone effects.

Transmutable viruses that effect creatures attacked buy infected creatures, like rabies and ghoul rot.  

Creature binding spells when two creatures are linked the share damage. or even linking creatures to zone items. even magical leash traps when a creature goes into a zone they are held to a certain radius till leash is dispelled or destroyed.

Tracking traps and seeking spell combo's. A trap that when activated the creature gets a magic mark and special tracking spells can home in onto that no matter where in the arena the creature goes the spell will follow. It may take a round or two before it hits (depending on the distance). there is nothing like trying to figure out how to save the creature/yourself from a clear and present doom.

Spells that stay in effect for multiple rounds and have Ricochet effect and random bounces. It can hit a creature, wall, or zone item and randomly bounce from there.

Mirror traps when an attack spell is casted across a zone the trap activates and reflects the attack back at the caster.

a Druidic thing but a leyline system where items, zone items, and some animals are connected and the more zone they cover create system of power and protection for the druid. The druid could use that direct line to cast spells trough healing item or creature in the area, cast deadly spores, or other nature effects.

walls that move like a big sawblade or blades that move across a wall line from one side of the arena to the other.

elemental creatures that can be either a wall or a creature, they morph!

creatures that can combine to make a more powerful creature. like an earth and fire elemental truns in to a magma creature.

Also want to say what a creative group of fans there are a lot of great ideas in the other pages really gets the creativity going.