i am level 80 level locked because i do not have cata.
can i still go to SM and kill the headless horseman for the hallows end seasonal event?
okay, so do i need to be in a party to do it?
because i went to SM and walked in and did not see the shrine

At 80 you cannot solo the horseman. You will need a group. You cannot queue for a random until you reach 84. You'll need to find 4 other people that are willing to carry you through. You must be in a group and use the dungeon finder to enter the instance to see the Headless Horseman.

You better run like the dickens ok and if it attacks cease you kill him and level gotten oh yah