Server Items & Server items exchange l2 high five karik

https://www.rpg-club.org/?p=market

Santa's Hat - Effect: +15 P.Def, +10 M.Def, afaik it also gives a speed, which is not written on this site.
90/90 means the item is limited, same as shadow weapon, when u get on zero, you cannot use it anymore. Some items have  this mp limit but you can still use them when it goes off. But if you see the same items and one of them is cheaper, it's obvious that you can use it for limited time.
About Robe of magic, I don't see it on the site and I don't have game installed atm to check it, but I guess you will use it as a cloak.