It is free and needs no download. The game runs in your browser on a custom WebGL engine, with no plugin, no installer and no account required.

Headshots deal 2.5 times normal damage. Because ammo is limited and waves keep coming, consistently hitting heads is the main way to keep up with the tougher enemies rather than an optional flourish.

Creepers rush in and explode, so kill them at a distance. Brutes glow red just before they charge. Hurlers leave orange rings on the ground where poison is about to land. Phantoms fly, so cover will not protect you from them.

A boss appears every fifth wave. Bosses change their attack pattern as they lose health, so the fight shifts through phases rather than repeating a single pattern.

Yes. Emeralds earned during a run carry over and can be spent on permanent upgrades in the Armoury, so every run contributes to your long-term progress.