  As a new two-dimensional Dirac material, 8-\textit{Pmmn} borophene hosts
novel anisotropic and tilted massless Dirac fermions (MDFs) and has attracted
increasing interest. However, the potential application of 8-\textit{Pmmn}
borophene in spin fields has not been explored. Here, we study the long-range
RKKY interaction mediated by anisotropic and tilted MDFs in magnetically-doped
8-\textit{Pmmn} borophene. To this aim, we carefully analyze the unique
real-space propagation of anisotropic and tilted MDFs with noncolinear momenta
and group velocities. As a result, we analytically demonstrate the anisotropic
behaviors of long-range RKKY interaction, which have no dependence on the Fermi
level but are velocity-determined, i.e., the anisotropy degrees of oscillation
period and envelop amplitude are determined by the anisotropic and tilted
velocities. The velocity-determined RKKY interaction favors to fully determine
the characteristic velocities of anisotropic and tilted MDFs through its
measurement, and has high tunability by engineering velocities shedding light
on the application of 8-\textit{Pmmn} borophene in spin fields.
