Thanks for all the comments, everyone. I am making mental notes, and as I continue to work on him, I may change my mind. But just to be clear, the only aspect of Carrion Swarm that I am concerned with is the self-healing, if you time it correctly and can apply it to multiple enemy heroes. The channel time, amount of damage, and duration seem fine to me for a tank, but the fact that he gets both the invulnerability and self-heal may be too good. Time will tell, as people get better at countering it.