The Blood Oath is a pact made by some gods, a vow to promote life and order in the world, a recognition of a higher calling than the petty squabbles that sometimes arose. This is a World Artifact.
The oath is a metaphysical object; it has no specific physical form but it lives in the bodies of those who have taken it upon themselves. Technically, it isn't even in their blood, as not all gods have blood.
In order to first gain access to the power of the blood oath, one must willingly bind one's self to it. Afterwards, one can draw forth its power by injuring one's self. It requires the spilling of blood, as it were.
By spilling their "blood," a god may tap into the power of the oath to receive a +pp towards Nourish or Spawn actions.
In order to use the power of the oath, one must injure one's self. This reduces one's combat rating by 1 for that week.
However, if one has bound one's self to the oath but intentionally creates or spreads chaos in the world, the power of the oath will turn on them. A wound will open and that god will suffer a -1 to their combat rating until they atone for their action(s).
The oath spawned Rampart, and the oath lives in him.
Umbart the Mighty has also willingly taken the oath upon himself.