The MiniBooNE experiment has recently reported an anomalous 4.5 \sigma
excess of electron-like events consistent with \nu_e appearance from a
\nu_\mu beam at short-baseline. Given the lack of corresponding \nu_\mu
disappearance observations, required in the case of oscillations involving a
sterile flavor, there is strong motivation for alternative explanations of this
anomaly. We consider the possibility that the observed electron-like signal may
actually be due to hypothetical new particles, which do not involve new sources
of neutrino production or oscillations. We find that the electron-like event
energy and angular distributions in the full MiniBooNE data-set, including
neutrino mode, antineutrino mode, and beam dump mode, severely limit, and in
some cases rule out, new physics scenarios as an explanation for the observed
neutrino and antineutrino mode excesses. Specifically, scenarios in which the
new particle decays (visibly or semi-visibly) or scatters elastically in the
detector are strongly disfavored. Using generic kinematic arguments, this paper
extends the existing MiniBooNE results and interpretations to exhaustively
constrain previously unconsidered new physics signatures and emphasizes the
power of the MiniBooNE beam dump search to further constrain models for the
excess.