Types of Creatures:

Creatures may have one or more tags. Tags are shown directly under the creature's name and level in square brackets and italics. Most tags have no effect by themselves, but many abilities can only effect certain types of creatures  that is, creatures with those tags. For example, the Animal Backup skill only allows you to have creatures with the [Animal] tag.

Sample Tags:

1.   Æther: Æther creatures are native to Æther. They are immune to the antimatter on the plane, which they can breathe as a normal human breathes air. Æther creatures can use the antimatter to become extremely powerful, and don't normally need to eat, drink, or sleep. They can still eat when they want to, though  which is whenever they see an intelligent, usually.
2.   Animal:
3.   Aquatic:
4.   Cold: the creature is, naturally or unnaturally, affiliated with cold and ice.
5.   Cold Immunity (Takes no damage from Cold-type attacks)
6.   Heat Weakness -3 (Takes 3 points extra damage from Heat-based attacks)
7.   Cannot cast any spell that deals Heat damage. If a creature gains the cold subtype and has spells that can deal heat-damage, the damage changes to Cold-type.
8.   Demon: See the Demon entry
9.   Electric:
10.   Electricity Immunity
11.   Digital: The creature is vulnerable to EMP and hacking. The DC to hack a digital creature is 3 + its Science (Computers) skill + its Intelligence. Nearly always coincides with soulless, nonliving, and usually nonintelligent
12.   Fey
13.   Fire: the creature is, naturally or unnaturally, affiliated with heat and fire.
14.   Heat Immunity
15.   Cold Weakness -3
16.   Cannot cast any spell that deals Cold damage
17.   Magical: Magical creatures are subject to certain laws. Who laid down these laws and why is a mystery, but a creature with the Magical type can€t even consider breaking them. Magical Creatures cannot:
18.   Cross a magic circle
19.   Enter a mortal€s home uninvited (once invited in a single time, the creature can return at will)
20.   Break an agreement, promise, or oath (although the creature can lie in other contexts, and can try to find loopholes)
21.   Magical Construct
22.   Nonintelligent: Nonintelligent creatures have the following traits:
23.   Intelligence of *
24.   Most nonintelligent creatures have a spirit of *
25.   Immune to fear
26.   Do not gain XP or levels. The skills they start with are the only ones they will ever have.
27.   Cannot take ranks in Ingenuity
28.   Emotionless: Emotionless creatures have the following traits:
29.   Immune to morale effects
30.   Cannot take ranks in Berserk, Faith
31.   Nonliving
32.   Immune to nonlethal damage, fatigue, poison, disease, hunger, thirst, suffocation, radiation
33.   Endurance of *. Gains +3 to toughness instead of adding its endurance (like an object) but uses its strength score for all other purposes.
34.   Rideable
35.   Summonable
36.   Undead
37.   Ghost
38.   Soulless: A soulless creature is devoid of a soul.
39.   Immune to Soul Comas and any morale effect that eventually causes one (such as a soul vampire€s or a ghost€s drain)
40.   Most spiritless creatures have a spirit of *
41.   Cannot take ranks in Magic Power, Faith, Mystic Focus
42.   Spirit: An insubstantial ghostlike creature. Unless otherwise mentioned, has the following characteristics:
43.   Can float in any direction at a speed of its Spirit score in squares, or walk at its normal speed.
44.   The creature can move through walls and floors as if they were insubstantial, or be constrained by them as if they weren€t (so, a moving ship wouldn€t leave one behind unless the spirit wanted it to).
45.   The spirit cannot move through cold iron or any material denser than platinum, but can move through silver (even silver as thin as a wire) instantaneously.
46.   Invulnerable/Spirit. Spirits can only be seriously threatened by other spirit creatures
47.   Vulnerability: Iron/Disruption. If the spirit is ‚hit€ with an iron weapon (all the attacker has to do is swing an iron object through the spirit. The spirit can dodge, but can€t block or parryƒ the weapon would go right through the spirit insubstantial shield or sword), then the spirit temporarily loses cohesion. It vanishes for 1d6 seconds before reforming. During this time, it can take no actions.
48.   Even if the creature is normally immune to diseases and poisons, Spirits are strongly affected by radiation. They get radiation sickness normally, and suffer a morale penalty for every failed fortitude check against radiation. Typically, spirits have other vulnerabilities based on radiation as well.
49.   If the spirit is ever affected by anything that would put it in a Soul Coma, it vanishes and is effectively dead.
50.   Spirit creatures can interact with other spirit creatures and objects as if they were solid.
51.   Has a Strength score of *. Spirits use their Spirit score instead. Spirits may or may not be able to move physical objects; unless otherwise specified they cannot.
52.   Spirits almost always a bonus to Possession.

Aquatic

1.   Water-Breathing: Aquatic creatures can breathe underwater the same as normal creatures breathe air, but start to 'drown' when pulled out of the water.
2.   Swim: Aquatic creatures get a swim speed of 2 squares and the corresponding +4 bonus to Athletics (swim) checks.

Note : This racial background is probably more suited to NPCs and monsters than player characters, except in very unusual aquatic campaigns.