Both Sol's Caldo Luce (-20%) and and Zephyrus's Infection Gale (-15%) are C frame. The wiki only says A doesn't stack with A while B doesn't stack with B. So maybe C stacks with another C.

Mordred's Outrage and Belphegor's Seven Deadly Sins are both B frame.

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I doubt she's coming for us yet because when DMM first release this union battle there was no reward.

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Quote Originally Posted by Inb4whales View Post
Next Gacha SSR Kamihime -
Attachment 5411

Next Union event SSR Eidolon -
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Discuss on whether or not they might be worth getting for the players who are choosing said element for their team.
I'll try and keep this first post updated as the updates keep rolling.
I doubt she's coming yet.