what exactly does crit do? double dmg?
Depends on Crit. I don't think any of them are double damage. For example, Asherah is low chance for 20% extra damage. But remind you, at least at the moment, there's nothing in the same modifier. So 20% more damage actually IS 20% more damage. For comparison, P2W Eidolons are ~25%ish more.
SSR Cybele is 35% damage I believe, but I don't know the procrate of that. I'd imagine it's low.
How does Crit stack? Uuuuh... I don't know. I have no idea. Can you proc multiple crits? Wait, no, the buff probably overwrites... can you have a Crit passive? Well, you can Crit from your weapon Grid at least... uh, yeah. I dunno.
Kamihime crit buffs will overwrite each other, depending on the damage bonus
Stinger stacks additively with itself (each instance of stinger being a separate roll)
I have zero clue how stinger and kamihime crit buffs interact with each other
Also, a reminder to the readers who forgot this: crits require elemental advantage
✦ Union Leader of Ixion (Kamihime Game ID#: 1318886 | Discord ID: VeryVoodoo#0081)
✦ Recruiting Active/Strong Players - Apply on Discord: https://discord.gg/kJdnGWq
Strictly speaking, that requirement is implied for stinger, because stinger is described as 'zokusei kyarakuta no kyuusho kougeki kakuritsu UP'. Zokusei kyarakuta is just the 'character of X element' part we see in every weapon skill. Kakuritsu's probability. 'kyuusho kougeki' is what we also see in abilities we refer to as crits, like Asherah's.