You pick a hero and walk into a field that's filling with monsters.

Your weapon swings on its own, so what you're really controlling is where you stand — funnelling the horde, staying out of the middle of it, and spending your abilities at the moment they're worth the most.

Kills drop experience. Experience means a level, and a level means three cards: a wider swing, a second blink charge, a poison that spreads on death.

You take one every thirty seconds or so, and by the end you're doing something the hero flatly could not do at the start.

Every round ends with a boss. Survive it and the next one starts harder.

Die — and you will — and whatever you earned buys permanent upgrades in the Sanctum before the next attempt.

Runs are short. Losing one is the normal outcome.