I love novel ideas for stalls! A good trick in these social media times is to make it photogenic, so that people will want to take selfies with it; also offering certificates saying things like "I tricked Santa" can bring them in. Another very important tip is to have a big sign saying what the stall is, so people can understand it at a glance: people might not try if they have to ask what to do.
Pin the nose on Rudolph is an easy one: you can make it more interesting by having the main prize for getting the nose in the right place, but other smaller prizes (such as sweets) for getting it on his head, antlers, eyes, and so on. Show this information on a sign.
Someone else I know did an interesting one: Can you trick Santa? Santa sat behind the stall, and would look at you for a few seconds, before pulling his hat over his eyes. You then had to ask Santa two questions about yourself, such as what shoes are you wearing, or what colour is your coat (there was a list of suggested questions). You won a prize if Santa got them both wrong! But Santa was good at observation, so the trick was to ask something really difficult, such as "how many lace holes are in my trainers?".
Another one was "Let it snow": a variation on the game of spoon cotton wool balls from one bowl to another. Each participant was blindfolded and given a big spoon, and had three goes to scoop cotton balls from a bowl into a hole in the top of a big box, so that they would fall down into a painted scene inside the box, like snow. They won a prize if they got a certain number of balls in. Again, selfies and certificates saying "I made it snow" made it really popular.