Taylor took to the stage in Tampa last night for the final stop of her 1989 North American tour. And while there were a lot of incredible celebrity Halloween costumes last night, we have to say that Swift nailed it, dressed as Olaf, the snowman from Frozen. To top it off, Idina Menzel (dressed as Elsa from Frozen, naturally) was one of the surprise guests of the evening. Add to that an army of reindeer-clad backup dancers while the two sang "Let It Go" to an audience of 55,000 people and you can see why Swift's costume was a success. Click below to see a clip of Swift in costume at her concert last night (via her Instagram)!