  Artificial lattices have been employed in many two-dimensional systems,
including those of electrons, atoms and photons, in a quest for massless Dirac
particles with flexibility and controllability. Periodically patterned molecule
assembly and electrostatic gating as well as moir\'e pattern induced by
substrate, have produced electronic states with linear dispersions from
isotropic two-dimensional electron gas (2DEG). Here we demonstrate that
massless Dirac fermions with tunable anisotropic characteristics can, in
general, be generated in highly anisotropic 2DEG under slowly varying external
periodic potentials. For patterned few-layer black phosphorus superlattices,
the new chiral quasiparticles exist exclusively in an isolated energy window
and inherit the strong anisotropic properties of pristine black phosphorus.
These states exhibit asymmetric Klein tunneling with the direction of incidence
for wave packet with perfect transmission deviating from normal incidence by
more than 50{\deg} under an appropriate barrier orientation.
