  The discovery of Weyl semimetals represents a significant advance in
topological band theory. They paradigmatically enlarged the classification of
topological materials to gapless systems while simultaneously providing
experimental evidence for the long-sought Weyl fermions. Beyond fundamental
relevance, their high mobility, strong magnetoresistance, and the possible
existence of even more exotic effects, such as the chiral anomaly, make Weyl
semimetals a promising platform to develop radically new technology. Fully
exploiting their potential requires going beyond the mere identification of
materials and calls for a detailed characterization of their functional
response, which is severely complicated by the coexistence of surface- and
bulk-derived topologically protected quasiparticles, i.e., Fermi arcs and Weyl
points, respectively. Here, we focus on the type-II Weyl semimetal class where
we find a stoichiometry-dependent phase transition from a trivial to a
non-trivial regime. By exploring the two extreme cases of the phase diagram, we
demonstrate the existence of a universal response of both surface and bulk
states to perturbations. We show that quasi-particle interference patterns
originate from scattering events among surface arcs. Analysis reveals that
topologically non-trivial contributions are strongly suppressed by spin
texture. We also show that scattering at localized impurities generate
defect-induced quasiparticles sitting close to the Weyl point energy. These
give rise to strong peaks in the local density of states, which lift the Weyl
node significantly altering the pristine low-energy Weyl spectrum. Visualizing
the microscopic response to scattering has important consequences for
understanding the unusual transport properties of this class of materials.
Overall, our observations provide a unifying picture of the Weyl phase diagram.
