Just something I cobbled together it doesn't all scan perfectly but I hope you enjoy!

On the 1st day of Christmas Harry gave to me a
Cloak of invisibility.

On the 2nd day of Christmas Harry gave to me
2 House Elves
And a cloak of invisibility

On the 3rd day of Christmas Harry gave to me
3 Pygmy Puffs
2 House Elves
And a cloak of invisibility.

On the 4th day of Christmas Harry gave to me
4 Horntails
3 Pygmy Puffs
2 House Elves
And a cloak of invisibility.

On the 5th day of Christmas Harry gave to me
5 Time turners
4 Horntails
3 Pygmy Puffs
2 House Elves
And a cloak of invisibility.

On the 6th day of Christmas Harry gave to me
6 Wands a-sparking
5 Time turners
4 Horntails
3 Pygmy Puffs
2 House Elves
And a cloak of invisibility.

On the 7th day of Christmas Harry gave to me
7 Quills a-scratching
6 Wands a-sparking
5 Time turners
4 Horntails
3 Pygmy Puffs
2 House Elves
And a cloak of invisibility.

On the 8th day of Christmas Harry gave to me
8 Owls a-swooping
7 Quills a-scratching
6 Wands a-sparking
5 Time turners
4 Horntails
3 Pygmy Puffs
2 House Elves
And a cloak of invisibility.

On the 9th day of Christmas Harry gave to me
9 Werewolves howling
8 Owls a-swooping
7 Quills a-scratching
6 Wands a-sparking
5 Time turners
4 Horntails
3 Pygmy Puffs
2 House Elves
And a cloak of invisibility.

On the 10th day of Christmas Harry gave to me
10 Ghost a-floating
9 Werewolves howling
8 Owls a-swooping
7 Quills a-scratching
6 Wands a-sparking
5 Time turners
4 Horntails
3 Pygmy Puffs
2 House Elves
And a cloak of invisibility.

On the 11th day of Christmas Harry gave to me
11 Hippogriffs bowing
10 Ghost a-floating
9 Werewolves howling
8 Owls a-swooping
7 Quills a-scratching
6 Wands a-sparking
5 Time turners
4 Horntails
3 Pygmy Puffs
2 House Elves
And a cloak of invisibility.

On the 12th day of Christmas Harry gave to me
12 Snitches flitting
11 Hippogriffs bowing
10 Ghost a-floating
9 Werewolves howling
8 Owls a-swooping
7 Quills a-scratching
6 Wands a-sparking
5 Time turners
4 Horntails
3 Pygmy Puffs
2 House Elves
And a cloak of invisibility.

Happy Christmas!!