Here is some work I did on monster subtypes, in case you wanted to add them.
I tried to make them as generic and True20 applicable as possible.
(I'd like to add the demon and devil subtypes, but by golly they aren't in the SRD!)
Air Subtype: This subtype usually is used for elementals and outsiders with a connection to the Elemental Plane Air. Air creatures always have fly speeds and usually have perfect maneuverability.
Angel Subtype: Angels are a race of celestials, or good outsiders, native to the heavenly planes.
Traits: An angel possesses the following traits (unless otherwise noted in a creature’s entry).
—Darkvision out to 60 feet and low-light vision.
—Immunity to acid, cold, and petrification.
—+2 to toughness to resist electricity and fire.
— +4 racial bonus on saves against poison.
—Protective Aura: Against attacks made or effects created by evil creatures, this ability provides a +4 deflection bonus to defense and a +4 resistance bonus on saving throws to anyone within 20 feet of the angel. Otherwise, it functions as a ward and the shining ward effect of the purifying light power (adept level equals angel’s level).
—Tongues: All angels can speak with any creature that has a language, speaking and understanding any spoken word. This ability is always active.
Aquatic Subtype: These creatures always have swim speeds and thus can move in water without making Swim checks. An aquatic creature can breathe underwater. It cannot also breathe air unless it has the amphibious special quality.
Archon Subtype: Archons are a race of celestials, or good outsiders, native to the heavenly planes.
Traits: An archon possesses the following traits (unless otherwise noted in a creature’s entry).
—Darkvision out to 60 feet and low-light vision.
—Aura of Menace: A righteous aura surrounds archons that fight or get angry. Any hostile creature within a 20-foot radius of an archon must succeed on a Will save to resist its effects. The save Difficulty varies with the type of archon, is Charisma-based, and includes a +2 racial bonus. Those who fail take a -2 penalty on attacks, defense, and saves for 24 hours or until they successfully hit the archon that generated the aura. A creature that has resisted or broken the effect cannot be affected again by the same archon’s aura for 24 hours.
—Immunity to electricity and petrification.
— +4 racial bonus on saves against poison.
—Protective Aura: Against attacks made or effects created by evil creatures, this ability provides a +4 deflection bonus to defense and a +4 resistance bonus on saving throws to anyone within 20 feet of the archon. Otherwise, it functions as the shining ward effect of the purifying light power (adept level equals archon’s level).
—Teleport: An archon can teleport itself and up to 50 pounds of objects at will. Archons can travel up to 1,400 miles when they teleport. Interplanar travel is not possible. There is no chance for the archon to arrive off target. In addition, the archon need not have seen its destination, but in that case it must have at least a reliable description of the place to which it is teleporting. If it attempts to teleport with insufficient information (or with misleading information), it disappears and simply reappears in its original location.
—Tongues: All archons can speak with any creature that has a language, speaking and understanding any spoken word. This ability is always active.
Augmented Subtype: A creature receives this subtype whenever something happens to change its original type. Some creatures (those with an inherited template) are born with this subtype; others acquire it when they take on an acquired template. The augmented subtype is always paired with the creature’s original type. A creature with the augmented subtype usually has the traits of its current type, but the features of its original type.
Cold Subtype: A creature with the cold subtype has immunity to cold. It has vulnerability to fire, which means it has a -5 to saves against fire, regardless of whether a saving throw is allowed, or if the save is a success or failure.
Earth Subtype: This subtype usually is used for elementals and outsiders with a connection to the Elemental Plane of Earth. Earth creatures usually have burrow speeds, and most earth creatures can burrow through solid rock.
Extraplanar Subtype: A subtype applied to any creature when it is on a plane other than its native plane. A creature that travels the planes can gain or lose this subtype as it goes from plane to plane. Monster entries assume that encounters with creatures take place on the Material Plane, and every creature whose native plane is not the Material Plane has the extraplanar subtype (but would not have when on its home plane). Every extraplanar creature in this book has a home plane mentioned in its description. Creatures not labeled as extraplanar are natives of the Material Plane, and they gain the extraplanar subtype if they leave the Material Plane. No creature has the extraplanar subtype when it is on a transitive plane, such as the Astral Plane, the Ethereal Plane, and the Plane of Shadow.
Fire Subtype: A creature with the fire subtype has immunity to fire. It has vulnerability to cold, which means it has a -5 to saves against cold, regardless of whether a saving throw is allowed, or if the save is a success or failure.
Native Subtype: A subtype applied only to outsiders. These creatures have mortal ancestors or a strong connection to the Material Plane and can be raised, reincarnated, or resurrected just as other living creatures can be. Creatures with this subtype are native to the Material Plane (hence the subtype’s name). Unlike true outsiders, native outsiders need to eat and sleep.
Shapechanger Subtype: A shapechanger has the supernatural ability to assume one or more alternate forms. Many magical effects allow some kind of shape shifting, and not every creature that can change shapes has the shapechanger subtype.
Traits: A shapechanger possesses the following traits (unless otherwise noted in a creature’s entry).
—Proficient with its natural weapons, with simple weapons, and with any weapons mentioned in the creature’s description.
—Proficient with any armor mentioned in the creature’s description, as well as all lighter forms. If no form of armor is mentioned, the shapechanger is not proficient with armor. A shapechanger is proficient with shields if it is proficient with any type of armor.
Swarm Subtype: A swarm is a collection of Fine, Diminutive, or Tiny creatures that acts as a single creature. A swarm has the characteristics of its type, except as noted here. A swarm has a single pool of levels, a single initiative modifier, a single speed, and a single defense. A swarm makes saving throws as a single creature. A single swarm occupies a 5-foot square (if it is made up of nonflying creatures) or a cube (of flying creatures) 10 feet on a side, but its reach is 0 feet, like its component creatures. It can occupy the same space as a creature of any size, since it crawls all over its prey. A swarm can move through squares occupied by enemies and vice versa without impediment. A swarm can move through cracks or holes large enough for its component creatures.
A swarm of Tiny creatures consists of 300 nonflying creatures or 1,000 flying creatures. A swarm of Diminutive creatures consists of 1,500 nonflying creatures or 5,000 flying creatures. A swarm of Fine creatures consists of 10,000 creatures, whether they are flying or not. Swarms of nonflying creatures include many more creatures than could normally fit in a 10-foot square based on their normal space, because creatures in a swarm are packed tightly together and generally crawl over each other and their prey when moving or attacking. Larger swarms are represented by multiples of single swarms. The area occupied by a large swarm is completely shapeable, though the swarm usually remains in contiguous squares.
Traits: A swarm has no clear front or back and no discernable anatomy, so it is not subject to critical hits. A swarm made up of Tiny creatures has a +5 bonus to toughness against slashing and piercing weapons. A swarm composed of Fine or Diminutive creatures is immune to all weapon damage. Reducing a swarm to 0 hit points or lower causes it to break up, though damage taken until that point does not degrade its ability to attack or resist attack. Swarms are never staggered or reduced to a dying state by damage. Also, they cannot be tripped, grappled, or rushed, and they cannot grapple an opponent.
A swarm is immune to any power or effect that targets a specific number of creatures (including single-target powers), with the exception of mind-affecting if the swarm has an Intelligence score and a hive mind. A swarm has a -5 to toughness against powers or effects that affect an area, such as splash weapons.
Swarms made up of Diminutive or Fine creatures are susceptible to high winds. For purposes of determining the effects of wind on a swarm, treat the swarm as a creature of the same size as its constituent creatures. A swarm rendered unconscious by means of nonlethal damage becomes disorganized and dispersed, and does not reform until its hit points exceed its nonlethal damage.
Swarm Attack: Creatures with the swarm subtype don’t make standard melee attacks. Instead, they deal automatic damage to any creature whose space they occupy at the end of their move, with no attack roll needed. Swarm attacks are not subject to a miss chance for concealment or cover. A swarm’s statistics block has “swarm” in the Attack and Full Attack entries, with no attack bonus given. The amount of damage a swarm deals is based on its levels, as shown below.
Swarm level = Swarm Base Damage
1-5 = +2
6-10 = +4
11-15 = +6
16-20 = +8
21 or more = +10
A swarm’s attacks are nonmagical, unless the swarm’s description states otherwise. Some swarms also have acid, poison, blood drain, or other special attacks in addition to normal damage.
Swarms distract foes whose squares they occupy, as described below.
Distraction (Ex): Any living creature vulnerable to a swarm’s damage that begins its turn with a swarm in its square is nauseated for 1 round; a Fortitude save (Difficulty 10 + 1/2 swarm’s level + swarm’s Constitution; the exact Difficulty is given in a swarm’s description) negates the effect. Using powers or concentrating on powers within the area of a swarm requires a Concentration check (Difficulty 20). Using skills that involve patience and concentration requires a Difficulty 20 Concentration check.
Water Subtype: This subtype usually is used for elementals and outsiders with a connection to the Elemental Plane of Water. Creatures with the water subtype always have swim speeds and can move in water without making Swim checks. A water creature can breathe underwater and usually can breathe air as well.