We consider 2d electrons moving in a magnetic field (Landau quantization problem) with a local disordered potential. For very light electrons the problem gets restricted to fluctuations around the ground state i.e. lowest Landau level (LLL). It was found by Brezin, Gross and Itzykson that there is an emergent supersymmetry at LLL that enforces dimensional reduction in certain observables. We re-explore this problem and map it to a more general “Parisi-Sourlas” SUSY theory which is usually associated to critical points of "random field” disordered models. We clarify how the SUSY features extend to a much larger class of observables and to higher Landau levels. Finally from the local supersymmetries of the problem we can write a set of new super-Ward identities that the disordered theory must satisfy.