|System Reference Document v3.5|
Action points give players some control over poor die rolls. Although this has little effect in an average encounter, it makes it a little more likely that characters will survive extremely challenging encounters and less likely that a single character will fall to what would otherwise be a balanced foe because of bad luck. A reserve of action points lets even careful players expose their characters to more risks, heightening the gameís tension and opening the door to even more heroic action. This variant also makes it less likely that an entire adventuring group will fall victim to one powerful effect, such as circle of death or cloudkill.
Action points also make it more likely that the use of a characterís most potent abilities will be successful. For example, although its overall effect on an encounter might be minimal, few things frustrate a paladin more than missing with a smite attack ó an event that becomes less likely when using action points.
That said, action points can also lead characters to routinely get in over their heads (relying on action points to save themselves), and for GMs to unconsciously increase the difficulty of encounters (since characters are more likely to succeed against foes of equal power). This is as fine as long as the characters have a reserve of such points to spend ó but if they run out, encounters that would otherwise be merely challenging can become incredibly deadly. Keep the number of action points available to your characters in mind when designing encounters.
For GMs who are worried that action points increase the power level of characters without an offsetting cost, thereís an easy solution. Just think of each action point as a one-use magic item with a broad range of possible effects. With that analogy, it becomes easy to justify reducing the amount of treasure awarded to balance out the accrual of action points. Note that this is merely a tool for GMs interested in carefully monitoring character power levels; action points should never be for sale.
An action point is roughly equivalent to a magic item worth 100 gp per character level (since the higher a characterís level, the more potent the effect).
Every time a character advances, he gains a number of action points equal to 5 + 1/2 his new character level. Some prestige classes might allow a faster rate of accrual, at the GMís option.add to a single d20 roll, to take a special action, or to improve the use of a feat.
You can spend 1 action point in a round. If you spend a point to use a special action (see below), you canít spend another one in the same round to improve a die roll, and vice versa.
Depending on character level (see table), a character might be able to roll more than one d6 when he spends 1 action point. If so, apply the highest result and disregard the other rolls. A 15th-level character, for instance, gets to roll 3d6 and take the best result of the three. So, if he rolled a 1, 2, and 4, he would apply the 4 to his d20 roll.
Activate Class Ability: A character can spend 1 action point to gain another use of a class ability that has a limited number of uses per day. For example, a monk might spend an action point to gain another use of her stunning fist ability, or a paladin might spend an action point to make an additional smite attack.
Boost Defense: A character can spend 1 action point as a free action when fighting defensively. This gives him double the normal benefits for fighting defensively for the entire round (+4 dodge bonus to AC; +6 if he has 5 or more ranks in Tumble).
Emulate Feat: At the beginning of a characterís turn, he may spend 1 action point as a free action to gain the benefit of a feat he doesnít have. He must meet the prerequisites of the feat. He gains the benefit until the beginning of his next turn.
Extra attack: During any round in which a character takes a full attack action, he may spend 1 action point to make an extra attack at his highest base attack bonus. Action points may be used in this way with both melee and ranged attacks.
Spell Boost: A character can spend 1 action point as a free action to increase the effective caster level of one of his spells by 2. He must decide whether or not to spend an action point in this manner before casting the spell.
Spell Recall: Spellcasters who prepare their spells in advance can spend 1 action point to recall any spell just cast. The spell can be cast again later with no effect on other prepared spells. This use of an action point is a free action and can only be done in the same round that the spell is cast. Spontaneous spellcasters such as sorcerers and bards can spend 1 action point to cast a spell without using one of their daily spell slots. This use of an action point is a free action and can only be done as the spell is being cast.
Improved Critical: You can spend 1 action point to double your critical threat range. Since two doublings equals a tripling, this benefit increases your threat range from 19-20 to 18-20, from 17-20 to 15-20, or from 15-20 to 12-20, including the effect of your Improved Critical feat. This benefit stacks with the benefit from Improved Critical, but not with other effects that increase threat range.
Metamagic Feats: You can spend 1 action point to add the effect of any one metamagic feat that you have to a spell you are casting. The spell is cast at its normal level (without any level adjustment because of the feat) and takes no extra time to cast.
Heighten Spell automatically raises a spellís effective level to the highest level of spell you are capable of casting. For example, if a 7th-level wizard with the Heighten Spell feat casts burning hands and spends 1 action point to heighten the spell, the spell is treated as if it were a 4th-level spell in all respects even though the wizard prepared it normally (as a 1st-level spell).