Monster Effects is a boutique guitar pedal builder founded in 2001 by electronics designer John Spears. The brand's reputation was built on the Swamp Thang, an all-analog tremolo pedal inspired by the brown-face Fender tremolo circuit, which became a staple on pedalboards of touring and studio guitarists looking for vintage-style tremolo in a hand-wired format.

The company's other well-known release is the Mastortion, a high-gain distortion pedal Spears designed in collaboration with Brent Hinds of Mastodon. Pedals are built in small batches in the United States and Canada, with production handled by longtime dealer Scott Hager after he took over manufacturing from Spears in 2019. Distribution and sales are managed through Axe...and You Shall Receive in Brantford, Ontario.

Monster Effects occupies a niche at the intersection of vintage-voiced modulation and heavier, artist-driven overdrive, with a catalog that stays deliberately small and focused on hand-built construction rather than broad product lines.

Monster Effects has 1 product cataloged on Equipboard, including Overdrive Effects Pedals. Their gear is featured by 1 artist, with the strongest followings in Rock. Notable users include Brent Hinds.