Ugh I gotta pick between an animalistic chosen or an undead one and I don't know which one would be more useful as a forsaken
How does this stack with animalistic chosen natuarlly dealing +50% by default? Do they stack linearly or multiplicatively?
"Dissociative Identity" Forsaken Distortion trait becomes "Dissociative Identity (Perfect Pet)": Instead of dealing +50% HATE and INJU damage, deals +50% for _all_ circumstance damage
Isn't it purely better than
"Flexible Peacemaker" Forsaken Distortion trait becomes "Flexible Peacemaker (Playful Energy)": While at 100% Stamina and above, species trait upgraded from +50% damage to +100% damage; However, when using this ability, deployment costs an extra +30% Stamina
Which is better depends on what you need. I'm generally a fan of filling out with Undead first as the most immediate need I have is for cheap Chosen that can reliably break T2 Circumstances. Undead can retain significantly more power while being cheap.
I wait until later to pick up Animalistic, as I make those a bit beefier so they can reliably hit 2 Circumstances (and usually help with a Distortion).
As for your comparison of the two, assuming you're making a Forsaken that hits 2 Circumstances, here's some relevant information.
If you take Dissociative Identity, your multipliers will stack in the following way: (100 + 50)% for Species, (100 + 50)% for your chosen two Circumstances, for a total of (1.5)(1.5) = 2.25x in those Circumstances, which can be whatever you wish.
If you take Flexible Peacemaker on Animalistic, your multipliers at 100% Stamina would be (100 + 100)% for species, (100 + 50)% for PLEA and INJU, for a total of (2)(1.5)= 3.0x in PLEA and INJU. But the rest of the time it'll be 2.25, same as the other.
There's more to consider than that, though. A Flexible Peacemaker will have very low Disgrace, and therefore can be quite high in cost. Prohibitively so, in fact, if she's got a DIG core--you'll just have to train Disgrace to whatever level makes her cost fit into your strategy, so you might not be able to use her for a while while she builds up her Disgrace.
There's also whether or not you have good Punishers to put on them that'll buff one or more of these damages or give her something useful. And, I don't know what damage types you might still need in your roster.