Our elves (we have 2, Holly and Snowball), kidnapped Barbie and tied her to one of DD's chairs with tinsel.
Scattered the DVD's round the lounge and were sitting in front of the TV with crisps and chocolate.
Wrote their names, and 'I was here' on the bathroom walls and mirror in toothpaste.
Toilet papered the bathroom
Sealed one of the doorways by christmas papering it up
Rode in one of DD's toy cars (i.e one for Barbie type dolls), and were found positioned at the top of a ramp about to drive down it
Were reading a story to all of DD's cuddly toys/dolls that were sat round listening
They had a bubble bath in a box (foam packing balls were the bubbles)
Helped themselves to the cereal (DD likes the boxes of individual cereals, so they had one each). They scattered it round the kitchen and made a mess.
Can't think of any more off the top of my head, but am looking for ideas for this year so will be watching with interest! I'm not sure I could get away with painting DD's nose without her waking up.