Map needs uniqueness

[:1]im making a fairly basic hero survival/race to kill all enemy style arena map, each player is secluded into there own little arena and in race you must kill the enemies b4 the other players, in survival you just survive.

Im thinking its to basic and i need something that will make it special, ill be making cutome heroes with custom abilities, special creeps and possiple random events.

Thx in advance

EDIT-thx blackflame but i already have a shop in each players arena and theres already a boss every 5 rounds(im not sure how much rounds there will be) and the AI idea is interesting, id put that in l8er as right now the waves arent really balanced or 'set in cement.|||maybe after a few different levels are cleared have a hidden door open that allows heroes to have access to a store where you can purchase unique items/abilities/upgrades. Additionally after surviving a sertain amount of time you could have a random item thrown in to make it more competitive.

An awesomely fun idea would of course be to have an end of round boss with its own trigger-made AI system for its abilities to make the fight feel more like you have a chance to beat him if you chose the right tactics rather than enemy stats vs your stats (which always seems to have the same outcome).|||terrain change maybe?|||heres a new idea: (Might even just be fun in some other type of map)

have a contained area set up with 4 or 8 pathways leading to it (like a plus sign ir a *) there will be a tower in the center and a crystal pylon at the end of each pathway (blocking it). Every point on that area will eventually spawn in a specific unit with a ranged attack that will charge a crystal pylon with ectricity that will power up the tower.

heres how it would work:

When a hero kills a unit, that specific ranged unit will get spawned into one of the 4 or 8 areas... (it rotates clockwise but stops spawning units when all areas are occupied) that unit will start attacking the pylon and when the pylon reaches 0 HP it's HP resets and becomes owned by that player.

When all Pylons are controlled by one player then it sets off a blast killing those ranged units and the tower becomes charged and a timer starts. For that duration that players hero/units gain a bonus. When that timer runs out the tower shuts down and the whole thing starts over again.

You could even do something like this just for a specific boss as a tatic...make him invulnerable or have a very high amount of armor and spawn enemies at the player to charge the tower and disable his defences for a brief period of time so you can beat him.