How the behaviour of $10^{23}$ particles follows from counting: microstates and Boltzmann's entropy, the microcanonical ensemble and what temperature is, the Boltzmann distribution derived from a heat bath, free energy as the competition between energy and entropy, equipartition, the ideal gas and the Gibbs paradox, Maxwell-Boltzmann speeds, fluctuations and the thermodynamic limit, the grand canonical ensemble, Fermi-Dirac and Bose-Einstein statistics, the degenerate Fermi gas, Bose-Einstein condensation, the Ising model and the transfer matrix, mean-field theory and its failures, critical exponents and universality, Landau theory, the renormalisation group, and the H-theorem.
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Every idea is taught with motivation and a worked example before the drills, and an FSRS spaced-repetition engine schedules each review for the day its model predicts you would forget it. A short placement check finds what you already know, so you start Statistical Mechanics exactly where it's useful.