How multiple initiatives affects CR

[Thealtruistorc]

I can't help but wonder this, given that I will be implementing it into a campaign soon. If a monster operates on multiple initiative counts or has two or three turns on a single initiative, how much more should it's CR be? I'm guessing that it would be CR +1 given a certain mythic template that replicates the ability somewhat, but that book has a reputation for containing poorly balanced material. What do you guys think?

[antoin]

It all depends on what this monster's abilities are. If it's just getting one more claw attack a round, yeah maybe CR +1. If it's another Eye Ray of Death, probably bump it up +3 at least. As a DM, I wouldn't worry too much about the numeric CR, but rather think, "What kind of challenge is this to the party? Does giving it multiple actions just add a little more fun or is this now possibly a TPK?"
Party size is also a big factor. A 6-person party shouldn't really have to worry about this. A 3-person party might die as a result.

[Crake]

Well, remember that 2 of the same creature is CR+2. A creature acting twice is similar to having 2 of them, but using the same hp pool, and being in the same position, and suffering from all the same conditions/effects. From that viewpoint, I think CR+1 is the logical place to put it, though I think I'd probably make it CR+1.5 (rounded down) per extra turn. So a creature that gets 2 extra turns per round is CR+3, not CR+2.

[OldTrees1]

A two-headed two-tailed bifurcated snake (http://theangrygm.com/return-of-the-son-of-the-dd-boss-fight-now-in-5e/) gets 2 initiative counts and has its CR calculated as if it were 2 snakes.

Assuming the extra turns come with extra hp pools and turns are lost as the hp pools disappear, then
2 turns: CR + 2
3 turns: CR + 3
4 turns: CR + 4
6 turns: CR + 5

[PraxisVetli]

What's the difference between 2 Inititives and someone rockin Greater Celerity or the like?

[Flickerdart]

Who was that guy that designed a monster that was really just two monsters? I wish I could find the article, it seems relevant here.

Anyhow, take the community CR calculation guidelines and run them for the monster, giving it half its HP, then add two because there are effectively two of this half-monster. The various advantages of having one body (less damage on AoOs, easier to hide) are countered by the various disadvantages (more vulnerable to SoLs, can't flank or aid another) more or less evenly.

[OldTrees1]

Who was that guy that designed a monster that was really just two monsters? I wish I could find the article, it seems relevant here.

I linked the two-headed two-tailed bifurcated snake above.