If you successfully complete the ritual, you can ask for one of the following
- Taming the Black Eel River.
Only if you took Black Eel water; allows for crossing of the river with exploration parties, war parties, or merchant caravans without incident.
- Taming the Oslira river.
Only if you took Oslira water; allows for crossing of the river with exploration parties, war parties, or merchant caravans without incident
- Protection from the forces of Water.
Will protect you from floods and water monsters for seven years
- Riches from below the waves.
Immediate 75 goods
Do note that as per all Rituals, even a successful completion will cost your clan magic. Taming the River costs you 3 points. Also as per all rituals, success of the ritual will improve clan mood, whereas failure will harm it.
Anyone may undergo the ritual. Unlike most rituals, all leaders are equally proficient at this quest, only their skills matter.
When you start the ritual, assuming you haven't tamed both rivers already, you will be asked if you want to use water from the Oslira or the Black Eel river. Performing the ritual with the Oslira river water is more difficult, and the only benefit is the ability to tame the Oslira river.
You will then be asked if you want to seek the aid of other Riders. Good relations will have other clans send aid, which will increase your chances of success at all of the ritual actions. Bad relations will get you ignored, or even mocked. You may then also ask the assistance of the Wheels, who have the same benefits but are harder to convince to help you. The more clans that are involved the greater the chance of success, but also the greater diplomatic stakes in the ritual; succeeding at this (or any ritual, for that matter) will increase the like and fear other clans have of you, but especially ones that partook in the ritual.
You will then be asked to make a sacrifice. This is a relatively simple ritual to perform, and the sacrifice can be smaller than other rituals without penalty. 8-10 goods/herds is often enough to avoid a penalty when dealing with the Black Eel river, and around twice that seems to be all that is necessary for the Oslira.
Unlike most rituals, Taming the River does not have a clear, linear progression. Instead, you will face three occasions in which Arcos tries to overflow its banks, and you must drive it back. Doing so successfully all three times will automatically pass the ritual; succeeding twice will usually pass it; fewer successes will usually cause the ritual to fail.
Each time, your quester will have five options to try to defeat Arcos, each of which can be used only once:
- Subdue the dragon by force.
This tests combat.
- Use cunning to defeat the dragon.
While not 100% clear, this seems to test a combination of leadership and bargaining.
- Trade valuables with the dragon.
This one tests bargaining, with some degree of influence by the amount you offer the dragon. It also gives you the opportunity to make a profit, whether you succeed or fail at keeping the dragon confined.
- Command the dragon to retreat.
This option tests leadership.
- Seduce the dragon.
It is unclear at the time of this writing (August 28th, 2018) what value this tests. If your ancestral enemies are the forces of Water, this option will be more difficult for the quester.
The options chosen by Reladivus were:
- Subdue by force
- Use cunning
- Trade valuables
There do not appear to be any bonuses for taking this path, so you should use whatever skills the individual heroquester is best at.