Kepler-36 is a Sun-like G-type star (about 1.03 solar masses, 5,979 K, 1.63 solar radii), 528 light-years from Earth. Kepler-36 b and c are a rocky planet and a puffy mini-Neptune separated by only about 0.01 AU, driving huge transit-timing swings. Kepler-36 b is a 3.8-Earth-mass planet, with an orbital period of 13.9 days, discovered in 2012 via transit. Kepler-36 c is a 7.1-Earth-mass planet, with an orbital period of 16.2 days, discovered in 2012 via transit. The planet was found when it crossed the face of its star, producing periodic dips in brightness that reveal its size and orbital period to space-based photometry. Mutual gravitational tugs between the planets can slowly reshape their orbits, preserving clues to the system's assembly.