Heyo, for the special abilities, I was thinking along the lines of being able to eventually make different illnesses depending on the race after getting stronger/later in the RP, but for the beginning I was thinking of an illness that can affect everyone, but affects humans/human like beings the most. The analogy that I have in mind is cowpox, a pretty bad disease for certain animals, but pretty mild for humans and other creatures like birds. But in this case, the illness would be more harmful for humans and be less harmful the less human-like the being is.

For the whispers ability, it's more of a mind virus kind of concept where the Pretender attempts to spread doubt, fear, and anxiety in the mind of a sentient being. Course, some people are more resistant/prone to this.

As for the blessing, I intended on making it very simple and weak early on. As you mentioned, its essentially a make them a little bit more lucky and a little bit healthier kind of deal. Later on, it could be more powerful like making them amazing at archery, but not in the beginning.

Personally, I was thinking about making the Pretender's power scale with the number of believers/followers he has. 

Let me know if there's anything else that I can clarify/change!