runescape

If you're talking about the Full Skeleton clothings... It's the holiday item of Halloween last year, you can't take it anymore if you didn't take it last year at the event =[

But if you're talking about Full Skull Sceptre (Skull Sceptre), you need to go to the Stronghold of Security to kill 4 kinds of monster in the 4 decks (level-12, level-28, level-49, level-75) and collect the 4 pieces of the broken sceptre (right skull half, left skull half, bottom sceptre, top sceptre) and use it to one to an other to connect them.

It was a holiday item last year...
there is no way to get it anymore now...

halloween special cloths(last year)