This is a bit embarassing for me, because i've been on this site nearly ten years, and I'm kind of never around for Morostide :o This year I'm trying to catch up with all the (still available) achievements, but I'm not sure about the battle achievements... Where can I find these opponents, are they random events, do I need items, are they even around this year?

When they become available during morostide there will be a news post

Right now they are holding off on battle stuff until they get the site to behave. But once they are ready to release the challengers we will be told via a news post. Usually we get challengers in pairs over the course of a week and have till the 31st to get wins in.

Thank you both! So it's just a matter of waiting, that's easy, haha :) Hope I can take on some of them~

There are quite a few opponents for this holiday, some easy ones and then some much harder ones. So you should be able to beat a few of them at least!

But yeah, there will be a news post (or multiple posts) whenever new challengers are released, and they'll show up in the Coliseum under the "Event" tab (next to the normal, secret, Cash Shop ones).

Right, when I saw the battle achievements I freaked out wondering how to complete them, then realized it might not be released yet XD we have to wait :P I so not ready for these waves tho lol.