The halloween one that I know of is called "You've been boo'ed".
I found this christmas one on the net which is the same idea.
Hope it's what you are looking for.

You have been Elfed!

SantaÂs little helper has come to town,
To leave these goodies you have found.
If you wish to have the best season of all
You must help this "Elf" with his call.

First, post this Elf where it can be seen
And leave it there till Christmas Eve.
Then other visiting Elves will pass on their way.
Be sure to participate, it will bring joy to your day..

Second, make two treats,
Two Elves, and
Two notes like this.

Just one day, is all youÂve got
So go ahead and give it a shot.

Leave the treats where they Elf has not gone
By the light of the moon, deliver to their home.

Hide behind a bush, a car even a tree
The surprise & joy on their face you are sure to see.

Now you've been blessed with yuletide cheer.
YouÂll feel it throughout the New Year.

Alas another Christmas Tradition is sure to have begun.
Thanks for sharing in this Christmas fun.

And last but not least, enjoy the season.
For all of the right reasons.

Happy Holidays!

Found this on a christian craft site - kinda like the "You've been booed"

The Christmas Angel has come to town,
To leave you some goodies, I see you have found.
If you wish to spread some of this good cheer,
Continue this greeting, 'cause Christmas is near.
First post the "Angel" where all can see,
And leave it there until Christmas Eve.
Then make 2 treats, with 2 notes like this,
Deliver to 2 neighbors who the Angel has missed.
You have only two days to leave a treat.
Ring the doorbell and run -- be fast on your feet.
Let's share in the spirit of friendship and love,
That's what Christmas is really made of.