Dark electro-pop maniac John Maus met almost across-the-board critical disdain with his first few albums, building a small but devoted cult following but failing to break through as a more widely accepted outsider artist until 2011's more realized We Must Become the Pitiless Censors of Ourselves made some critics change their minds about Maus. That album's cold sheen and sometimes oddball updates on obscure '80s synth pop sounds didn't stray too far stylistically from earlier Maus albums, but something about its character was more consistent and digestible than the sometimes scattered feel of his first two records. Where those could feel zany or annoying, Pitiless Censors felt serious and deliberate even in its weirdest moments. Given his slow arc toward consistent presentation of his solo work, a collection of rare or unreleased recordings from between 1999 and 2010 could possibly highlight Maus' weakest traits. Luckily, A Collection of Rarities and Previously Unreleased Material doesn't come off far different from much of Maus' recorded output. More than half of the tracks are from a time following his bewilderingly brilliant 2007 album Love Is Real, and tunes like 2010's "Castles in the Grave" and 2008's "My Hatred Is Magnificent" feel like demo predecessors or outtakes to the manic high-energy synth pop that gelled so well on Pitiless Censors. With only a few exceptions, the further back the songs go the more interesting they get, as with 2003's infectious electro-funk romp "The Law" or the theatrical "Big Dumb Man." The early-2000s tracks are incredibly lo-fi, reminding us that Maus got his start as a collaborator with Ariel Pink's early homespun disco as well as the then often goofy Animal Collective. The greatest curiosity on the collection is "Fish with Broken Dreams," a remarkably melodramatic piece from 1999 with over the top yet surprisingly clear vocals and an artificial MIDI orchestra. The song isn't good, per se, but its inclusion is an interesting choice, illuminating just how long Maus has been a genuine freak. A Collection of Rarities gathers the different eras of Maus' strange and sometimes beautiful journey, from his tape hiss-saturated keyboard self-help sounds to the coldly uncomfortable late-night neon funk of "Rock the Bone." This compilation won't do anything to make Maus' bizarre intentions more clear or his cloudy legacy more cohesive, but for those already converted, its 16 songs will be essential. For everyone else, these deranged soundtracks and head-scratching dance jams are probably the straightest material Maus has to offer, and they straddle the same line between grating and unintentionally brilliant that he's been riding his entire career.