My winning strategy:
Element: Nature + ice (equally, until there was a skink). Storm 2 times. Nature and ice 15. Astral to 15. Storm to 15. Iron up to 15.
Skink (very good keeps on lower levels, ~ 120).
Spell carry: Frozen Spirit
Carry: Bonk, the Living Mountain
Wol'jin the Witch Doctor, the Astral rift, Icy Flower Ice Mine and others.
The towers were built so that the aura of the Skink acted on 15 towers.
Throughout the game you were rearranging items to Carry, depending on the type of creeps to beat stronger.
Tried to put the towers on the massive slowdown. Built 3 Bonk, the Living Mountain.