There are eight stages in the initial release of the game. The character cannot proceed to the next level before beating the current level. The eight levels are reminiscent of Ragnarok Online.
* Prontera Field Mini-bosses: Willow, PecoKnight w/ Poring Train, Rocker, Ambernite, Pupa/Creamy, Boss Monster: Eclipse * Sograt Desert and Ant Hell Mini-bosses: Golem, Hode Boss Monster: Phreeoni, Maya * Payon Cave Mini-bosses: Munak & Bongun, Greatest General, Ninetails, Sohee Boss Monster: Wolyafa (also known as Moonlight Flower) * Orc Village Mini-bosses: Orc Lady Boss Monster: Orc Hero * Undersea Tunnel Mini-bosses: Obeaune, Thara Frog, Penomena, Boss Monster: Deviace * Geffen Tower Mini-bosses: Giant Whisper, Marionette, Jakk, Nightmare Boss Monster: Doppelganger * Mt.Mjolnir and the Labyrinth Forest (Hidden Temple) Mini-bosses: Ground Petite & Flying Petite, Baphomet Jr. Boss Monsters: Mistress, Baphomet * Prontera City Boss Monsters: Eclipse, Maya, Moonlight Flower, Orc Hero, Deviace, Doppelganger, Baphomet, and the "Kafra"
There is a secret 9th level in Prontera City which is unlocked if all previous eight levels have been beaten with the Novice class.
* Prontera Castle Boss Monsters: 100 BOT and 1 BOT with aura
The first expansion, RBO Extra Scenario Vol. 1, was released on August 14, 2005. Scenario Vol. 1 added two new stages, an arena mode with 50 stages (10 of them are unlocked by finishing the previous 40 with each class), some character balances, and increased difficulty such as doubling boss and mini-boss damage.
A second expansion, RBO Extra Scenario Vol. 2, was released on December 29, 2005. Scenario Vol. 2 added three new levels, decreased the requirements for unlocking the extra arenas from all classes to two classes, and further tweaked gameplay.
The third expansion, RBO Extra Scenario Vol. 3, was released on May 21, 2006. Scenario Vol. 3 added one new level.
RBO Extra Scenario Vol. 1Edit
* Prontera Culvert Mini-bosses: Female Thief Bug & Male Thief Bug, Cramp Boss Monster: Golden Thief Bug * Sunken Ship Mini-bosses: Mimic, Ghostring, The Wanderer Boss Monsters: Drake * Arena Mode
RBO Extra Scenario Vol. 2Edit
* Lutie and the Toy Factory Mini-Bosses: Chepet, Angeling, Christmas Jakk Boss Monsters: Hatii, Stormy Knight * Pyramid Mini-Bosses: Minotaur, Ancient Mymmy, Isis Boss Monsters: Amon Ra and Osiris * Sphinx Mini-Bosses: Minotaur, Pasana, Marduk Boss Monsters: Pharaoh
RBO Extra Scenario Vol. 3Edit
* Amatsu and Tatami Maze Mini-Bosses: Shinobi, Tengu Boss Monsters: The Paper and Incantation Samurai