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Deep underground a giant crystal is all that stands between the cavern and the dark. Creatures pour out of the tunnels on both sides, crawling, flying, digging and smashing their way towards it. Steer the crystal's beam, build machines and hold the line for as long as you can.

BEND THE BEAM
• The crystal fires a beam of light straight up through the cavern
• Place mirrors on sockets and turn them in 22.5° steps to steer it
• The beam burns and pushes back every creature it touches
• Unlock prisms that split the beam into two paths
• Rock blocks the light, so every cavern is a new puzzle

BUILD AND POWER MACHINES
• Tesla coils zap the nearest creature
• Rock crushers roll heavy boulders across the ledges
• Frost vents slow everything around them
• Machines spend crystal energy, but aim the beam at one and it runs free at double speed
• Upgrade machines up to Mk 3, repair them when brutes smash them

GATHER ENERGY
• Defeated creatures drop energy shards; tap them before they fade
• Energy trickles from the crystal and pays out for every cleared wave
• Spend it on mirrors, machines, repairs and abilities
• Call the next wave early for bonus energy

SIX KINDS OF CREATURES
• Crawlers, armoured beetles, flying bats and leaping jumpers
• Diggers tunnel through rock and open new paths
• Brutes stop to wreck your mirrors and machines
• Every wave is bigger and tougher and opens more tunnels

ABILITIES AND CAVERNS
• Overcharge doubles beam power, Quake hurls creatures into the air, Stasis freezes the swarm
• Three caverns: Amethyst Hollow, Mossglow Shafts and Ember Vault
• Survive deeper to unlock new abilities and caverns

UPGRADE AND COLLECT
• Earn coins for waves, kills and shards
• Permanent upgrades: crystal health, beam power, starting energy and a shard magnet
• Four crystals, each with its own beam colour
• Best scores and deepest waves saved on your device

Music and sound effects with separate switches, no internet connection required.

How deep can you hold the cavern?