Ultimate is the fourth difficulty and is accessable to all characters at level 80. On offline single mode on GameCube and Xbox versions of PSO, players enter Ultimate mode simply by defeating Dark Falz on Very Hard, regardless of level.
- Nearly all monsters, in addition to receiving upgraded stats and drops to accommodate the new difficulty, receive a graphical makeover. Some monsters gain entirely new characteristics, or existing characteristics change. For example, Chaos Sorcerers will become Gran Sorcerers, which, instead of attacking with Rafoie and Gibarta (or Gizonde in the Spaceship), will attack with Grants and Megid.
- In Episode I, the four main areas (Forest, Caves, Mines and Ruins) receive a graphical makeover.
- In Ultimate mode, players can earn rare items as rewards from the Soul of a Blacksmith quest.