Alien form

While bound to Zceryll, you gain the pseudonatural template(page 161 of Complete Arcane).

Pseudonatural Template (Complete Arcane, p161)
Can be applied to any corporeal creature
Size and Type: Type changes to Outsiders
Special Attacks: Once per day, a pseudonatural creature can cast True Strike on itself as a supernatural ability.
Special Qualities:
Resistance(Ex): A pseudonatural creature has a resistance to acid and electricity based on the base creature’s Hit Dice, see table below.
Damage Reduction(Ex): A pseudonatural creature gains damage reduction based on the base creature’s Hit Dice, see table below.

Hit Dice Acid, Electricity DR
1-3 5 -
4-7 5 5/magic
8-11 10 5/magic
12< 15 10/magic

Spell Resistance(Ex): The creature gain a SR of 10 + Base Creatures’s HD (Maximun 25)
Alternate Form(Su): As a standard action, a pseudonnatural creature can take the form of a grotesque,tentacled mass (or another appropriately gruesome form, as determined by the DM). Despite the alien appearance, it’s abilities remain unchanged. Other creatures receive a -1 morale penalty on their attack rolls against a pseudonatural creature when it is in this alternate form.Abilities: Same as base creature but Intelligence is at least 3.
Mindsight (Lords of Madness, p126): A creature that has this feat can detect and pinpoint beings that are not mindless (Anything with an Intelligence score of 1 or higher) within range of its telepathy. This works much like blindsense – the creature knows what square each thinking being is in, but it does not see the being and the being still has total concealment unless the creature can see it by some other means.The creature also perceives several observable characteristics about each being detected with mind sight,including the being’s type and intelligence score. The creature need not take any additional or special actions to gain this information; it is as obvious to mindsight as the being’s race and clothing would be to eyesight.

Alien form

Greyhawk(Pathfinder) PillanPatera