BestReviews is reader-supported and may earn an affiliate commission. Details. Here’s how to get the Squishmallows Advent calendar before you’re too late. If you’re planning to count down to the holidays with an Advent calendar this year, the time to buy it is now. These festive gifts are insanely popular, and the best ones sell out early. And if you have a Squishmallows fan in your household, you’re going to want to really act fast because there’s a Squishmallows Advent calendar that’s definitely going to sell out – and soon.