-I can definately see those spires that spew out water overloading and spewing so much water it knocks units nearby into the water.
-The center tiles of a different color, they need to do something evil - perhapes pop up without warning throwing units on top of it high into the air.
-You definitely need some spike traps, perhapes make the tiles drop out under units subjecting them to spikes
-Try arcing some lightning between those pillars
-Those trees need to cause some pain some how, perhapes make coconuts fall out of them.
-Flood the whole thing, thats nice and evil
-Have some geysers shoot up out of the water projecting rocks into the air
-Make the tiles outside the area in the center pop up trapping the players in there, then you can either let them battle it out in close confines or start some more carnage.
Just some ideas