The body is a vehicle for the soul, however, nowhere is it written that a body may have only one passenger. A Vessel is an individual who shares its body, either willing or otherwise, with another soul. Sometimes the two souls fight for control of the body, and other times the two souls live harmoniously together. This is always a product of the relationship between the two souls.
A Vessel can use the other soul in their body to their advantage. However, every time they do, they risk that soul taking control of their body. In a synergistic relationship, this may not be a big deal, but since all control is handed over, it could be disastrous for two souls who do not agree. Every time a Vessel uses an ability from this Overlay, they must make a DC 5 Wisdom Save or lose control of their body for 1d4 hours. Every time they make the Save, the DC increases by 1. When they fail the save, the DC resets to 5.
The Vessel had Advantage on Intelligence Skill Checks.
At Level 5:
- The Vessel can call upon their passenger to take the brunt of an attack. Once per Long Rest as a Reaction, the Vessel can negate all damage and effects during a round.
At Level 10:
- Once per Long Rest as a Bonus Action, the Vessel can siphon power from their passenger to overpower their opponents. Until the end of their turn, the Vessel doubles all their ability scores.
At Level 15:
- Once per Short Rest as a Bonus Action, the Vessel can call upon their passenger to give the effects of having had a Long Rest.
At Level 20:
- Once per Long Rest as a Bonus Action, the Vessel allows their passenger to take the brunt of all attacks, gaining invulnerability from all damage and effects for one hour.
- The Aspect of the passenger can manifest. Once per Long Rest as an Action, the passenger becomes a spectral vision behind the Vessel attached to its back. The Aspect acts on orders of the Vessel and is at full power while under command.
- The Vessel no longer needs to make saves against losing control.