For those who have the same doubt I've had - Can ally Gandalf (Over Hill and Under Hill #10) target himself with Narya (The Grey Havens #15), exhaust for the cost and then ready for the effect, thus gaining +1 atk and +1 def until the end of the phase? Here's what Caleb said:

Yes. Gandalf must exhaust in order to trigger Narya’s effect, therefore he is a valid target when you resolve its ability.
Cheers,
Caleb