Current Harrow Points:
Constitution Re-rolls: spend a Harrow point to re-roll one d20 roll modified by Constitution (a Fortitude save, etc.). You must use the second result, even if it's lower, though if you have multiple harrow points you may use them to get multiple re-rolls.
Fast healing: spend a Harrow point after resting for at least 1 minute to catch your breath and recover, healing a number of hit points equal to your current character level and 1 point of ability damage (not drain).
Damage Reduction: spend a Harrow point to gain DR 3/-. This effect persists for the duration of your current encounter.