  In recent experiments, external anisotropy has been a useful tool to tune
different phases and study their competitions. In this paper, we look at the
quantum Hall charge density wave states in the $N=2$ Landau level. Without
anisotropy, there are two first-order phase transitions between the Wigner
crystal, the $2$-electron bubble phase, and the stripe phase. By adding mass
anisotropy, our analytical and numerical studies show that the $2$-electron
bubble phase disappears and the stripe phase significantly enlarges its domain
in the phase diagram. Meanwhile, a regime of stripe crystals that may be
observed experimentally is unveiled after the bubble phase gets out. Upon
increase of the anisotropy, the energy of the phases at the transitions becomes
progressively smooth as a function of the filling. We conclude that all
first-order phase transitions are replaced by continuous phase transitions,
providing a possible realisation of continuous quantum crystalline phase
transitions.
