We discuss a minimal singlet-scalar extension to the Standard Model that achieves a strong first-order electroweak phase transition. The singlet can be naturally light because of an approximate shift symmetry and no extra hierarchy problem beyond that of the Standard Model Higgs is introduced. The baryon asymmetry of the universe may be explained by local electroweak baryogenesis arising from a coupling between the singlet and weak gauge boson. The predicted electron electric dipole moment is much below the current bound. Strong first order can be achieved from MeV-scale light scalar and small mixing with the Higgs. The viable parameter space can be probed by the observations of rare Kaon decay and the cosmic microwave background. A parity-symmetric model solving the strong CP problem is also discussed. The mixing angle is predicted for a scalar with a mass around 10 GeV or 10 MeV.