  The 8-\textit{Pmmn} borophene is one kind of new elemental monolayer, which
hosts anisotropic and tilted massless Dirac fermions (MDF). The planar
\textit{p-n} junction (PNJ) structure as the basic component of various novel
devices based on the monolayer material has attracted increasing attention.
Here, we analytically study the transport properties of anisotropic and tilted
MDF across 8-\textit{Pmmn} borophene PNJ. Similar to the isotropic MDF across
graphene junctions, perfect transmission exists but its direction departures
the normal direction of borophene PNJ induced by the anisotropy and tilt, i.e.,
oblique Klein tunneling. The oblique Klein tunneling does not depend on the
doping levels in \textit{N} and \textit{P} regions of PNJ as the normal Klein
tunneling but depends on the junction direction. Furthermore, we analytically
derive the special junction direction for the maximal difference between
perfect transmission direction and the normal direction of PNJ and clearly
distinguish the respective contribution of anisotropy and tilt underlying the
oblique Klein tunneling. In light of the rapid advances of experimental
technologies, we expect the oblique Klein tunneling to be observable in the
near future.
