He is not viable outside Arena or Ranked but god*, is he amazing in those scenarios.

A friend of mine has this Orochimaru and he basically never loses in Arena because of it. The ability to resurrect a dying unit with Hashirama is invaluable.

The main problem is that his mystery is not prompt, so it's easy to stop it if you're careful.

By the way, as a side note, Hashirama's mystery isn't supposed to do a lot of damage. It's supposed to immobilize two random units. The damage is just extra.