Beamhold

Beamhold is a tower defence game with a single light beam instead of towers. A crystal fires the beam across the field, and every path cell it crosses burns whatever walks there. Place mirrors to bend it, flip them with a tap, and route the beam along the path rather than across it, but each bounce and each cell of travel costs some power. Each wave earns another mirror; splitters that fork the beam arrive after wave 2 and amplifiers that make it strong enough for armoured invaders after wave 4. Hold four fields of eight waves each, ending with a boss on every field and a spiral path that leads to a gate in the middle. It plays in the browser with a keyboard, mouse or touch.