Momentum has been accumulating to consider high-energy muon collider as a future high-energy collider possibility, especially on US soil. Muon collider has unique physics cases, both as a Higgs factory and a high-energy lepton collider. In this talk, I will review the overall physics pictures for muon colliders and discuss these unique physics cases. In particular, I will show recent studies on WIMPs, Top Yukawa, Heavy Neutrinos, etc. We show that through some uniquely new channels, the muon collider could provide unprecedented information about broad classes of new physics, which can serve as a physics driver case for high-energy muon colliders.