Three unusual austins-type meroterpenoids penicianstinoids C-E (1-3) were obtained from the mangrove-derived fungus Penicillium sp. TGM112. The structures of 1-3 including absolute configurations were determined by detailed NMR, MS spectroscopic data, X-ray diffraction analysis, and calculated electronic circular dichroism data. Penicianstinoid C (1) was the first austins-type meroterpenoid with a unique 6/6/6/5 rearranged tetracyclic skeleton possessing two unusual spirocyclic moieties (2-oxaspiro[5.5]undeca-4,7-dien-3-one and 6-methylene-2-oxaspiro[4.5]decane-1,4-dione). Penicianstinoid D (2) was an unusual austins-type meroterpenoid with a 6/6/6/6 tetracyclic skeleton containing an octahydro-2H-chromen-2-one unit. Penicianstinoid E (3) possessed a 6/5/6/6/6/5 fused hexacyclic skeleton with an uncommon five-membered ether ring system. The plausible biosynthetic pathway of 1-3 is also proposed. Compounds 1 and 3 inhibited the growth of newly hatched Helicoverpa armigera Hubner larvae with IC50 values of 100 and 200 μg/mL, respectively.