Upon being reduced to 1/2 of your total Vitality Point value (including temporary VP), you become Fatigued. Spending a full round action to recover removes the effect, as does any magical healing received.
If a creature takes damage greater than 1/2 its total Vitality Point value (including temporary VP), they must make a Reflex save with a DC equal to the damage taken or 15, which ever is lower. If it fails, the creature is Flat-Footed until the beginning of its next turn. Feats or abilities that prevent a creature from being considered Flat-Footed apply as normal.
A natural roll of 1 on an attack roll results in a fumble. Roll 1d6
|1||Fall Prone, lose further actions|
|2||Overextend – Provoke Attacks of Opporunity, lose further actions|
|3||Drop Weapon, lose further actions|
|4||Take damage equal to your Str bonus (min 1), lose further actions|
|5||Lose further actions|
If a natural 20 is rolled to confirm a critical hit, a third attack roll is made to confirm an Instant Kill. If this attack roll succeeds, the target is instantly slain. This rule does not apply to creatures more than one size category larger than the character.
The ability linked to a skill is not set in stone. Some uses of a skill rely on different abilities (i.e. Instincts aren’t necessarily helpful when searching a complicated library for information, but experience noticing details is still helpful. You could make a Perception check utilizing INT in place of WIS; similarly, if two characters are competing in a public debate over some facet of history, they might make opposed Knowledge(History) rolls utilizing CHA in place of INT).
Skill challenges reflect situations in which the party must work together to accomplish a goal or overcome a problem that doesn’t involve fighting; yet it is general enough that it doesn’t require a specific skill check to be made. A locked door is not a skill challenge, picking the lock is a specific skill, and breaking it down is not a complimentary effort.
An example might be making a ship ready to sail: Profession Sailor could be used by one character to direct activities, Survival could be used to ready ropes, Climb could be used to rig sails, Knowledge(Engineering) could be used to check blocks and the hull. Craft(Smithing) could be used to repair a chain, forge an anchor, or brace a mast.
Success is determined by the group making a target number of successful checks before a specified number of failures. An easy challenge might have an average DC of 10, with a target of 5 successes before 10 failures, or DC:10 (5/10)