I watched a cartoon in the early 90's that was had in an episode a horned demon woman who kidnapped a blonde boy. The two of them discovered Atlantis and awoke his latent magical abilities. The boy then discovered Merlin was one of his past lives, and using the combined powers of himself and his past lives was able to free himself of the woman.

Does anyone know what I'm talking about?

Heman?

A young boy with the powers of Merlin
A demonic woman

Sounds like,.

DarkStalkers

view intro (http://www.youtube.com/watch?v=wHq_O5FFTec)