A one-thumb arcade game with a sharp core loop

ECHO is a deep-sea sonar arcade game. You are a bioluminescent sonar core at the bottom of the ocean — tap to emit sonar pulses that destroy incoming abyssal threats. Features the ECHO RESONANCE system: chain 4 kills to charge a free secondary echo wave that sweeps wider than your normal pulse. 4 enemy types (Shoal, Barb, Abyssal, Kelp), proximity-based chain scoring, ABYSSAL SURGE events, and local high-score persistence. Cyan/teal bioluminescent aesthetic on deep ocean void.