Elements: Fire (DoT), Ice (Slow), Lightning (Chain), Earth (Stun AoE). Click element then tier to build. 3 upgrade tiers each.
Synergies: Adjacent towers of compatible elements gain bonuses! Fire+Ice=Steam (AoE), Fire+Lightning=Plasma (pierce), Ice+Earth=Avalanche (stun+slow), Earth+Lightning=Magnetize (pull).
Enemies have resistances: Fire Slime (immune fire), Ice Golem (immune ice), Storm Spirit (immune lightning), Stone Golem (immune earth).
Boss at Wave 20: Resists ALL elements. Build diverse!