Van der Waals (vdW) heterostructures with two-dimensional crystalline materials offer an idealized experimental platform with an atomically sharp and clean interface to investigate emerging spintronic and superconducting devices. For example, vdW interfaces ensure that low-dimensional magnetic materials maintain their intrinsic spin-polarized electronic states and spin-flipping scattering processes at a minimum level, a trait that can expand spintronic device functionalities. In addition, vdW superconducting qubits prove that the ultraclean interfaces with single crystalline quantum materials are imperative for high-coherence solid-state quantum computing platforms. Here, using a vdW assembly of ferromagnetic Fe₃GeTe₂ (FGT) and semiconducting WSe₂ or hBN, we demonstrate electronically tunable, high-transparent spin injection across the vdW interface. By changing an electric bias, the net spin polarization of the injected carriers can be modulated and even reversed in polarity, which leads to a compelling sign change of the tunneling magnetoresistance. The unique spin polarization reversal can be attributed to sizable contributions from high-energy localized spin states in the metallic ferromagnet, so far inaccessible in conventional magnetic junctions. Additionally, we will share our preliminary results on vdW Josephson junctions made of superconducting NbSe₂ and non-superconducting FGT and MoS₂ spacers.