Darkvision is the extraordinary ability to see with no light source at all, out to a range specified for the creature. Darkvision is black and white only (colors cannot be discerned). It does not allow characters to see anything that they could not see otherwise—invisible objects are still invisible, and illusions are still visible as what they seem to be. Likewise, darkvision subjects a creature to gaze attacks normally. The presence of light does not spoil darkvision.

These planar travelers like to slip between the folds of space to attack enemies as though from thin air. They can cross from the Ethereal Plane with a move action but take 2 rounds to cross back, during which time they are immobile. As a xill fades away, it becomes harder to hit: Opponents have a 20% miss chance in the first round and a 50% miss chance in the second. A xill can planewalk with a willing or helpless creature.

Spell resistance is the extraordinary ability to avoid being affected by spells. (Some spells also grant spell resistance.)

To affect a creature that has spell resistance, a spellcaster must make a caster level check (1d20 + caster level) at least equal to the creature’s spell resistance. (The defender’s spell resistance is like an Armor Class against magical attacks.) If the caster fails the check, the spell doesn’t affect the creature. The possessor does not have to do anything special to use spell resistance. The creature need not even be aware of the threat for its spell resistance to operate.

Only spells and spell-like abilities are subject to spell resistance. Extraordinary and supernatural abilities (including enhancement bonuses on magic weapons) are not. A creature can have some abilities that are subject to spell resistance and some that are not. Even some spells ignore spell resistance; see When Spell Resistance Applies, below.

A creature can voluntarily lower its spell resistance. Doing so is a standard action that does not provoke an attack of opportunity. Once a creature lowers its resistance, it remains down until the creature’s next turn. At the beginning of the creature’s next turn, the creature’s spell resistance automatically returns unless the creature intentionally keeps it down (also a standard action that does not provoke an attack of opportunity).

A creature’s spell resistance never interferes with its own spells, items, or abilities.

A creature with spell resistance cannot impart this power to others by touching them or standing in their midst. Only the rarest of creatures and a few magic items have the ability to bestow spell resistance upon another.

Spell resistance does not stack. It overlaps.

Benefit

You get a +4 bonus on initiative checks.

Benefit
The creature’s secondary attacks with natural weapons take only a -2 penalty.

Normal
Without this feat, the creature’s secondary attacks with natural weapons take a -5 penalty.

Benefit
Penalties for fighting with multiple weapons are reduced by 2 with the primary hand and reduced by 6 with off hands.

Normal
A creature without this feat takes a -6 penalty on attacks made with its primary hand and a -10 penalty on attacks made with its off hands. (It has one primary hand, and all the others are off hands.) See Two-Weapon Fighting.

Special
This feat replaces the Two-Weapon Fighting feat for creatures with more than two arms.

Your Dexterity score increases by 2, and your Constitution score increases by 1.

Xill are usually 4-5 feet tall

You know Common and Infernal