Hi, I'm kinda new to this site so I don't really know how this works: I have all of them amulet except for the rainbow one, can I mix them to get it? Or something like that? Thanks :)

No, the Rainbow mage Amulet is an item that was in one of the donation presents in the cash shop, a couple years ago.

The only sure, gambling-less way you can get one is to buy it from another user.

The Hustler has a chance of selling them for 250 CSC too.

http://subeta.net/cashshop.php?act=hustler

"Can I interest you in a Rainbow Mage Amulet for only 250 Cash Shop Credits? Act now because I only have 20 left!"

Oh, I see! haha thank you so much!! :) You just solved a big doubt I have had long time now haha :D