You learn to use a supernatural ability of an assumed form.
Prerequisite: Wis 13, ability to assume a new form magically.
Benefit: You learn to use а single supernatural ability of another kind of creature while assuming its form through a polymorph spell or a similar effect. The saving throw DC against this ability is based on your ability scores, not those of a standard creature of the kind whose form you've assumed. For a breath weapon, the saving throw DC is 10 + your Constitution modifier ½ your Hit Dice (rounded down). For all other supernatural abilities, the saving throw (if any) DC is 10 + your Charisma modifier + ½ your Hit Dice (rounded down).
If a creature, such as an undead, has no Constitution score, use its Charisma modifier or its Constitution modifier (+0 for a nonability), whichever is higher, to determine the save DC.
Using this alien ability is disorienting. You take a −2 penalty on all attack rolls, saving throws, skill checks, and ability checks. Additionally, in a stressful or demanding situation (such as combat), you must succeed on a Will save (DC 19) or be unable to use the ability.
Normal: Without this feat, you cannot use the supernatural abilities ofacreature whose form you assume.
Source: Savage Species, page 30.