The Level Sphere is a highly important item that first appeared in Disgaea 3: Absence of Justice.
As its name would imply, the Level Sphere adds extra levels to the item that the player is leveling up through the Item World. However, in order for the Level Sphere's effect to work, the sphere has to be lifted by one of the player's units before the floor ends (by either reaching the gate or killing all other enemies). The floor also has to be cleared for their effect to work so using a Mr. Gency Exit will not grant the player the extra level gain. The Player can also get one Level Sphere through Reverse Pirating Missions.
Level Spheres come in three colors.
Green Spheres have a chance to spawn within the item from floor 20 onwards, and add five levels. Although there's usually one at a time, sometimes two will appear. They also appear in Survival Mode. If the player obtains 7 Level Spheres they can enter a Mystery Room and choose to skip 30 floors, revive a dead character or recruit Pleinair.
Yellow Spheres add ten levels, but can only be found in Reverse Pirating Missions.
Red Spheres add fifteen levels, but like the Yellow Spheres, only appear during Reverse Pirating Missions. They are rarer than the Yellow Spheres.
Level Spheres also appear in Disgaea 2: Dark Hero Days. Unlike in Disgaea 3 they appear Blue. Be warned, enemy units will attempt to destroy them, just like the item chests, so the player needs to work quickly to secure them. The enemies also tend to target the Level Sphere first.
They also appear in Disgaea 4: A Promise Unforgotten functioning the same way they did in Disgaea 3. They appear more commonly in the Item Growth Route. Like in Disgaea 3 Yellow and Red Level Spheres only appear while Reverse Pirating.
In Disgaea 3: Absence of Detention Green Level Spheres appear a lot more often and up to 4 can appear at any one time.