Elf - The use of forced perspective
As you can see in the images below, forced perspective was a go-to filmmaking trick for Jon Favreau and his team to create many of the shots early in the film where the oversized Buddy struggles to fit in with Santa's elf community. For those who have studied filmmaking, using forced perspective for shots like this shouldn't come as much of a surprise as you've seen countless examples of it over the years in films like The Lord of the Rings.
However, as simple as it seems, it is always impressive to see in action. It's hard to see for sure, but the top image above appears to come from this behind the scenes series on the making of Elf. You can watch part 1 here, but the scenes in the elf community are show (briefly) in this part 2 video below as First Assistant Director Jim Brebner explains his role and some of the shots which they're trying to get.