Mtg can you regenerate protean hydra?

Regeneration won't work on Protean Hydra for damage. Because of the replacement effect that removes counters instead of having damage dealt to it Protean Hydra is not "destroyed" by combat damage but instead put into the graveyard as a state based effect for having zero toughness. However, I believe you would still gain the life because Heal the Scars has you gain the life when the spell resolves, not when the creature would be regenerated. If you play the Heal the Scars before the combat damage step (which is when you should play it anyway) then the Hydra still has all it's counters and you will gain all that life.

Snakeform would make the Hydra a 1/1, normally the Hydra is a 0/0. Snakeform would not remove any of the counters so the Hydra would be a 1/1 with X +1/+1 counters on it. This might actually be a nice way of saving a Hydra from dying if all it's counters are removed. Since all the damage is prevented then being a 1/1 wouldn't kill it while being a 0/0 would. I'm fairly certain the Hydras ability adding twice as many counters back on would happen before the Snakeform effect would wear off. Might have to go look for an official ruling on that one though.