This thesis consists of two parts. In the rst part we examine pole-skipping, a phenomenon observed in thermal Green's functions in quantum eld theories with gravity duals. We begin by analysing the near horizon behaviour of bosonic elds in asymptotically Anti-de Sitter spacetimes before presenting the detailed analysis of fermionic elds in such backgrounds. We nd that at negative imaginary Matsubara frequencies and special values of the wavenumber, there are multiple solutions to the bulk equations of motion that are ingoing at the horizon and thus the boundary Green's function is not uniquely de ned. At these points in Fourier space a line of poles and a line of zeros of the correlator intersect and we derive the generic form of the Green's function near such locations. We then consider explicit examples where the correlator is known explicitly and also discuss the special case of a fermion with half-integer mass in the BTZ background. In the second part we study the microscopic degrees of freedom of a particular black hole through the lens of the fuzzball proposal. In particular we construct a new class of smooth horizonless microstate geometries of the supersymmetric D1-D5-P black hole in type IIB supergravity. We rst work in the AdS3 S3 decoupling limit and use the fermionic symmetries of the theory to generate new momentum carrying perturbations in the bulk that have an explicit CFT dual description. We then use the supergravity equations to calculate the backreaction of these perturbations and nd the full nonlinear solutions both in the asymptotically AdS and asymptotically at case. These new geometries have a simpler structure than the previously known superstrata solutions. We conclude with a discussion and an outlook for possible generalizations of the results.