You and another willing, corporeal, living creature of the same or smaller size fuse into one being. As the manifester, you control the actions of the fused being. However, you can give up this control to the other creature. Once you give up control, you cannot regain it unless the other creature relinquishes it.
The fused being has your current hit points plus the other creature's current hit points. The fused being knows all the powers you and the other creature know, has the sum of your and the other creature's power points, and knows or has prepared any spells you or the other creature possesses (if any). Likewise, all feats, racial abilities, and class features are pooled (if both creatures have the same ability, the fused being gains it only once). For each of the six ability scores, the fused being's score is the higher of yours and the other creature's, and the fused being also has the higher Hit Dice or manifester level—this effectively means the fused being uses the better saving throws, attack bonus, and skill modifiers of either member, and it manifests powers at the higher of the manifester levels that you or the other creature possessed before becoming fused.
You decide what equipment is absorbed into the fused being and what equipment remains available for use. These fused items are restored once the power ends.
When the power ends, the fused being separates. The other creature appears in an area adjacent to you that you determine. If separation occurs in a cramped space, the other creature is expelled through the Astral Plane, finally coming to rest materially in the nearest empty space and taking 1d6 points of damage for each 10 feet of solid material passed through.
Damage taken by the fused being is split evenly between you and the other creature when the power ends. You do not leave the fusion with more hit points than you entered it with, unless you were damaged prior to the fusion and the fused being was subsequently healed. In a like manner, the fused being's remaining power points are split between you and the other creature (you can leave with more points than you entered with, as long as you don't exceed the maximum power points for your level and ability score). Ability damage and negative levels are also split between you and the other creature. (If an odd number of negative levels or ability score reductions must be split, you decide whether you or the other creature receives the additional loss.)
If a fused being is killed, it separates into its constituent creatures, both of which are also dead. You cannot use fission on a fused being.