It will cost $9.99 (about £6).
We've covered Crawl extensively before, but here's the gist: One player fights a slew of monsters in a randomly generated dungeon while three of their friends play as ghosts trying to stop them. The ghosts can inhabit monsters and traps and whenever someone succeeds at slaying the hero, they become human and assume that role instead. The first player to reach level 10 as a hero can go on the the boss: a monstrosity controlled by all three of the rival players.
Players level up in both human and non-human form. The hero can gain new attacks and spells, while the ghosts can inhabit increasingly powerful creatures in their quest to take the hero's place.
For more information on Crawl, here's a video detailing its skeleton enemies. In fact, there's a whole series of videos examining each type of monster in this complex arcade brawler.