The most well-known traveler from the Ethereal Plane is the phase spider, but other insect-like creatures with similar abilities have been seen jaunting in and out of the Material Plane. Planar scholars have put forth the theory that somewhere off the Ethereal Plane a demiplane exists that is home to what they call phase vermin (or phase creatures).
Phase creatures are mottled black or gray and white in color, which may be an indicator of the nature of their home environment. They closely resemble normal vermin of the Material Plane, except that their natural weapons are inexplicably smaller. The phase creatures have adapted to this difference, however, with poison that is much stronger.
“Phase Creature” is an inherited template that can be added to any vermin (referred to hereafter as the base creature). A phase creature retains all the base creature’s statistics and special abilities except as noted here.
CR: Same as the base creature +2.
AC: The base creature’s natural armor increases by +1.
Defensive Abilities: The phase creature retains all the defensive abilities of the base creature, except it loses the “vermin traits” immunities and gains the following:
A phase creature can shift from the Ethereal to the Material Plane as a free action, and shift back again as a move action (or during a move action). The ability is otherwise identical with ethereal jaunt (caster level 15th).
Speed: the base creature’s land speed increases by 10 feet.
Attacks: The base creature retains all its natural attacks; however, the damage die of every attack reduces by one step (see the table below), but never below 1d2.
Special Attacks: A phase creature retains all the special attacks of the base creature. Saves have a DC of 10 + 1/2 phase creature’s HD + phase creature’s Constitution modifier unless stated otherwise. Base creatures with a poison special attack, recalculate it as below:
If the base vermin has poison, increase its poison damage by one step (1d3 becomes 1d4; 1d4 becomes 1d6, and so on). For example, if a Large vermin deals 1d4 points of Dexterity damage; a Large phase version of the same creature deals 1d6 points of Dexterity damage.
Feats: A phase creature gains Improved Initiative as a bonus feat.