Let's assume a good cleric tries to heal a hurt Dhampir, not knowing they are a Dhampir or not knowing about their "Negative Energy Affinity". So they Channel positive energy or use e.g. Cure Light Wounds. What happens:
- Dhampir is healed
- Dhampir takes damage (but gets a saving throw)
Also, if the Dhampir is not healed, would the cleric notice that it didn't work as expected?
The reason I'm asking is that according to the Channel Energy description a cleric has to choose whether to heal or damage undead, they can't do both:
A good cleric (or one who worships a good deity) channels positive energy and can choose to deal damage to undead creatures or to heal living creatures.
But cure light wounds says it heals living creatures and damages undead. But I remember reading another description of cure light wounds that said you can choose whether to heal or harm (like you do with Channel Energy). Maybe that was from a or DnD edition?