1. In the Halloween Event how do you get the pelt,candle anlters,and skull mask?

The zombie pelt, skull, and antlers can be obtained by casting the spell you want onto the Big Zombie Deer (Velocity). The spell will bounce back to you and give you the pelt/antlers/mask, depending on which spell you put on him.

2.Where does the "king deer" usually stay?

Velocity is often at the playground or graveyard, but his location can be pretty much anywhere, really.