Are you sure?
Because:
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For "dark character attack up" --> google translater "Attack of Light/Dark attribute character up"
For "elemental attack up" --> google translator "Increase in dark attribute attack" or "dark attribute attack power up"
At the moment I am thinking that Trivia offers 40% Dark attack up and not for dark characters....
Believe me I would love to have Echidna/Ouroboros for the time being but Jewel gatcha won't give me a SSR Eido :P
And yes I, too, won't spend my money to get one of those P2W Eidos, just for miracle ticket's. They are nice to have and will make your life a lot easier. But with elemental advantage you can also clear the harder content (Guild Orders, Tower) without them, that's what I think, don't know if it's true... ^^
Jack O'Lantern is also a good option because I can sell those Lilim Eidos, rehab and other upcoming SSR Event Eido I won't use.