This willingness to play with and challenge expectations and traditions, even as they created a legacy, is one of Andi Toma and Jan St. Werner's most enduring and endearing traits. A kind of musical birthday party with guests including their closest friends and collaborators as well as admirers, 21 Again shares the celebratory, experimental spirit of Mouse on Mars' best work (and also the two-day festival they curated as part of this anniversary). In terms of the duo's most recent output, the wide-ranging collection's tone falls somewhere in between Parastrophics' cerebral hijinks and WOW's free-for-alls, but it touches on almost every era of St. Werner and Toma's work in some fashion. "Shoe Fly," a collaboration with Tortoise, lives up to expectations: it's elegant and a little hyperactive, with prickly guitars giving way to a duel between the drums and synths. Modeselektor and Mr. Maloke help the duo indulge its most playful side on "Purple Fog," while Laetitia Sadier contributes a horrifying yet philosophical Marxist parable, "My Toe Is on Fire,