Extremal black holes are known to develop a horizon instability in the presence of scalar matter. In this talk, I will discuss how this picture extends to charged perturbations, which can trigger new instabilities via both gravitational and electromagnetic interactions. In particular, I will demonstrate that on a fixed background metric, charged matter can accumulate on the event horizon of an extremal Reissner-Nordstrom black hole without decaying, thus posing a new challenge to black hole stability. I will then present a numerical evolution of the same problem in the nonlinear setting, where metric backreaction is included. Under certain conditions, the accretion and scattering of charged matter can trigger nonlinear instabilities in a manner that electrically neutral matter cannot. These results shed light on the nature of the extremal horizon and have implications for the more astrophysically relevant Kerr problem.