Complex sentence: In May 2015, the duo returned to Monstercat with a Remix of Karma Field's "Build the Cities", as well as a single in December called "Signs" (feat. Shantee).
Split into simpler sentences: In May 2015, the duo returned to Monstercat with a Remix of Karma Field's "Build the Cities". In December 2015, the duo returned to Monstercat with a single called "Signs" (feat. Shantee).