Giving creatures regeneration

[CoI]

What would the boost to their cr be? If I added it as a mythic monster ability would you count it as 1 or 2 mythic abilities? Say MR x 2? Or do you think that'd be too much?

[Drahliana Moonrunner]

CoI wrote:

What would the boost to their cr be? If I added it as a mythic monster ability would you count it as 1 or 2 mythic abilities? Say MR x 2? Or do you think that'd be too much?

If it does not add meaningfully to it's combat abilities... None. The ability you're probably looking to add is Fast Healing. Which may not give it any boost at all considering the damage that mythic players can lay out.

[Maezer]

Honestly I wouldn't get too hung up on CR. CR paints with a very broad brush.

Instead look at your party and determine what kind of difference do you think the change will make to the encounter. For the most part regeneration is just a few extra hit points. Once a creature is unconscious its generally pretty trivial to keep unconscious for long periods of time.

Can the creature act while below 0 hp? If yes, then regeneration can be very significant.

Is the regeneration vulnerable to something the party has easy access too? Regeneration (fire) you can generally expect your party to have. Where as regeneration (Sonic) might be harder to cancel.

Does the creation have a valid escape mechanic? If it can teleport, go invisible, or fly etc. then its ability regeneration is much more likely to come into play.

Try to guess how much adding regeneration will change the encounter and adjust the CR based on that. Rather than looking for a universal regeneration is worth CR +x