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You can use an action point to improve a d20 roll by an additional 1d6. The 1d6 is rolled when the d20 is rolled. At level 8 (I think), this increases to 2d6 and, at level 15, to 3d6.

In addition, a /day character ability (e.g. barbarian rage, bardic music and so on) can get an extra use per day by the sacrifice of 2 action points.

For Strange Loopers, you can burn an action point to get an additional use of your 'ringmark' or dragonmark. Likewise, you can sacrifice a daily use of your 'ringmark' or dragonmark to activate the other.

You can also use an action point to stabilise while at negative hp. As a house rule, I also allow the use of half that level's allocation of action points (rounding down) to deflect certain death (e.g. huge damage, disintegration) and convert it to being stable at -9hp.

You get action points equal to 5 plus half your character level, rounded down (i.e. 5 at level 1, 6 at level 2 and 3, and so on). Any unused action points are lost at levelling up - i.e. you cannot have more than that level's allocation (normally - there are feats which can impact on this). Use 'em or lose 'em.

The details are in the ECS. These rules differ from the ones in the SRD (they are much more limted in scope in the ECS).

You can use action points only once per round.

-yanked from Aubrey; some modification for Strange Loops.