Flare (20s CD): Illuminate entire map for 3 seconds. Bonus points for NOT using flares!
Lanterns (10g): Place on path for small permanent light. One-time use per placement, 3 per wave.
Night creatures: +50% HP when in darkness. Shadow enemies invisible even in light.
Bats: Fly over towers, attack light sources. Werewolves at wave 10+.
Day/Night cycle: Every 5th wave is "day" - full vision! Otherwise night.
Defend through day and night cycles with different enemy behaviors. Night enemies are stronger but give more rewards. Cyclical defense game about timing and preparation.