Abstract: This talk explores scattering processes into final states containing a large number of particles, \((n \gg 1)\), in a four-dimensional massive scalar quantum field theory. I will begin by reviewing known results for tree-level and loop-level amplitudes at and near the multi-particle mass threshold in the limit \((\lambda \to 0)\) with \((n \sim E/m \to \infty)\). Since such high-multiplicity processes ultimately require a non-perturbative treatment, I will then present a semiclassical calculation valid in the weak-coupling, large-multiplicity regime with \((\lambda n \gg 1)\). We will discuss the apparent explosive growth of partial decay widths of highly virtual particles near (n)-particle thresholds, the interplay between the Higgsplosion and Higgspersion mechanisms, and the consistency of these phenomena with the unitarity of the theory.