One new pyridinone alkaloid pseudogymnone A (1) and one new tricyclic polyketide penijanthinone C (2), together with six known compounds, harzianic acid (3), 3-methyl-2-(2-nonenyl)-4(1H)-quinolinone (4), emodic acid (5), alaternin (6), violaceol-I (7), and violaceol-II (8), were obtained from the Cordyceps-colonizing fungus Pseudogymnoascus roseus. The structures and absolute configurations of the isolated compounds were elucidated through a combination of NMR and MS spectroscopic analyses, ECD calculations, and X-ray crystallography. Compound 3 exhibited obvious cytotoxicity against A549 (IC₅₀ = 4.2 µM) and MGC (IC₅₀ = 3.8 µM) cell lines. Integrated network pharmacology and molecular docking analyses indicated that compound 3 exerts potential anti-gastric-cancer effects by modulating multiple cancer-related signaling pathways, with EGFR identified as a potential target of compound 3.