This week's grossly oversinplied heresy comes courtesy of Pelagius, hence the name.
Pelagianism was refuted by St. Augustine of Hippo. Pelagians argued against the concept of original sin and that men are not corrupted by the sin of Adam. In essence, God created man is His image and gave us everything we need in order to achieve salvation by our own free will. Man has an inherently good nature. God demands perfection and it was in Jesus that we achieve a good example as opposed to the bad example that Adam set for us.
Augustine best rebutted this heresy by quoting (and going a little overboard with it) that "for all have sinned and fall short of the glory of God (Rom 3:23)." Grace has little to do with salvation according to pelagianism, hence the heresy.
Congratulations to this week's winner.