reaper soraka

You should be able to, yes. Additionally, it'll also pop up in sales and generally around Halloween time as well.

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Just to let you know Susanoo is definitely being accurate here, you can check out the Legacy & Limited Skins list here; https://support.riotgames.com/hc/en-us/articles/201752944#h1q4

Legacy Skins above 520 RP (I don't think any are under that) can be earned through Hextech Crafting and Mystery boxes, and you can see that Reaper Soraka is on that list under the Holiday > Harrowing section. Limited skins can't be earned through it and very rarely come back, but also as Susanoo stated, Legacy skins often return for their associated holiday.

I got this skin through hextech crafting, so yeah it's possible.