Across:

1 Shell Cottage
5 Herbology
6 Snape
8 Warbeck
10 Thestral
11 Azkaban
13 Pheonix
14 Bludger
15 Hogsmeade
16 Griffin

Down:

2 Expelliarmus
3 Transfiguration
4 Polyjuice Potion
7 Patronus
9 Whizzard
10 Voldemort