Energy System: Every tower consumes power. Build generators (+5 energy each, 40g) to supply them. If consumption exceeds supply, towers fire at 50% speed.
Beam (75g, 2NRG) - Continuous damage laser. Tiers: Focused Beam → Death Ray
Pulse (60g, 1NRG) - AoE burst around tower. Tiers: Shockwave → Nova
Railgun (120g, 4NRG) - Line penetration, pierces enemies. Tiers: Heavy Rail → Gauss Cannon
EMP (80g, 3NRG) - Stuns enemies in area (no damage). Tiers: Disruptor → Overload
Enemies: Drone (fast/weak), TankBot (slow/tank, beam resistant), StealthBot (invisible, only hit by Pulse), HackerBot (disables nearest tower)