Unlocking "Elemental Wave"

[Grayson Carlyle]

I saw this card once, though I can't remember where. I could have unlocked it by choosing my mage for the option, but did not at that moment.
Does anyone know what event unlocks this card, where it is and if there are any requirements?
Would really appreciate any help, after many runs I still can't find it again.

[Corence]

The Purple Rarity Temple event in the green portal (Nagas offer to teach you an ability) offered this to my Cornelius. Might also work with Evelyn?

[Grayson Carlyle]

Thank you. Gonna try and find the event. Don't remember seeing a purple event there, probably why I did not find it again.