The material below is Open Game Content from a 3PP Source
Suction (Ex): An eidolon can create powerful suction against any surface as it climbs, allowing it to cling to inverted surfaces with ease. An eidolon can establish or release suction as a swift action, and as long as it is using suction, it moves at half speed. Because of the suction, the eidolon’s CMD score gets a +10 circumstance bonus to resist bull rush, awesome blows, and other attacks and effects that attempt to physically move it from its location. Only eidolons with the aquatic, serpentine, or ooze base forms can select this evolution.