I love the nose painting idea, am going to try that this year.
From previous years particularly memorable ones are:
Building a Christmas tree from lego
Elf playing with barbies
Elf in a bath of marshmallows
Elf decorated DD's dolls house with Christmas decorations
Elf writing with red and green M&Ms
Elf reading mini Christmas books
Elf on his own bike sitting next to DC's bikes
Elf found sleeping in his own sleeping bag
This year elf is decorating kitchen with frozen themed decorations
And this year for the first time boy elf is going to be accompanied by a friend - girl elf. They each have personalised jumpers and aprons.
God, when I write this down I sound like I have a screw loose. I don't honestly.