Devolution

Transmutation
Level: Artificer * 3, Sorcerer */Wizard * 3, Summoner * 3
Components: V, S, M (a chameleon scale)
Casting Time: 1 Standard Action
Range: close (25 ft. + 5 ft./2 levels)
Target: one eidolon
Duration: 1 round/level
Saving Throw: Will negates
Spell Resistance: yes
  This spell causes an eidolon to lose one evolution plus one additional evolution for every five Caster Levels. Evolutions with the highest total cost are lost first. If there is a tie, randomly determine which is lost. If this spell causes an eidolon to fail to meet the prerequisites for other evolutions or abilities, those evolutions or abilities are lost as long as this spell persists.