Happy Halloween! Please check that your gates are locked, your walls are manned and your pumpkins are accounted for, because The Battle For Halloween has started.

Seven walls. One long night. Your job is to hold the white city of Dawnspire until dawn, while thousands of skeletons, zombies, witches and giants storm the gates. You can join the defence right now at battleforhalloween.tripgeo.com, in your browser, with nothing to install.

Everything in that trailer was rendered by the game itself: the footage, the music and the sound.

Castle Siege: hold the walls until dawn

The main event is Castle Siege. You defend Dawnspire, a white citadel cut into the mountain in seven walled tiers, from a grey afternoon until dawn. Between waves you build and repair. During them the Hallowhost comes at you with grave ladders, battering rams, siege towers and flaming pumpkin trebuchets.

As the night goes on, the waves get worse. There are thunderstorms, fire portals, werewolves, broom witches and vampire knights, and after midnight come the titans and the Headless King. He carries his own head. It is on fire. We would not describe him as approachable.

A very large monster manual

There are 71 unit types in the game, with thousands of units on the field at once, fighting in formations, complete with morale and routs. On one side you'll find skeletons, zombies, pumpkinheads, mummies, ghosts, banshees, werewolves, vampires, witches, stitched giants, magma and storm golems, the Headless Horseman and the Grave Titan. On the other are knights, pikes, archers, crossbows, priests, witch hunters and great cannons, who would all quite like to go home.

Ten ways to spend the night

A full Castle Siege is a long game, so there are plenty of shorter ways in. Try Quick Battle, Endless Night, Dominion, a 10-night Campaign, Scenarios, the Daily Battle, the Sandbox or an AI Tournament. If you'd rather not be responsible for anyone at all, pick Watch a Battle, pour yourself something warm, and let the AI armies fight it out while a cinematic camera follows the action.

On difficulty, Trick is the easy setting and Fright is a fair fight. The game plays best on a desktop or laptop in Chrome or Edge, and there are no touch controls yet, so leave your phone in the keep.