The Colosseum is Ragnarok Online II's equivalent of Ragnarok Online's Battlegrounds. It is a unique player-versus-player (PVP) scenario that allows players to fight one another in addition to monsters and rank up.
The ArenaColosseum uses an arena setting so that all players interested in PVP can go to one centralized area to fight. Whenever Colosseum opens up, a little notification will appear on every player's interface. Clicking on the notification will send them to the Colosseum arena.
By participating in the Colosseum, players can earn Blood Points, which can be used to purchase Colosseum items, gear, and mounts. Everything you kill, from monsters to players, will earn you Blood Points.