Pyrolysis is a promising feedstock recycling method for converting diverse plastic wastes—including polyethylene (PE), polypropylene (PP), polystyrene (PS), polyvinyl chloride (PVC), and polyethylene terephthalate (PET)—into valuable fuels and chemicals. Product yields are highly dependent on feedstock composition. Polystyrene consistently yields the most liquid oil (up to 70%), rich in valuable aromatics. Polypropylene also provides high oil yields (up to 90%), with its oil having physicochemical properties closest to diesel. Catalysis, particularly with zeolites (ZSM-5, NZ), is shown to be essential for lowering reaction temperatures and steering selectivity toward high-value aromatics (BTX). Furthermore, co-pyrolysis of plastics with biomass (e.g., wood) reveals non-additive synergistic effects that reduce char residue and enhance carbon conversion. This synergy is proposed to be physical for PP and PET (melt-phase interaction) but chemical for plastics like polycarbonate, which show an overlapping activation energy distribution with biomass. Also, the produced liquid oil possesses a high heating value (HHV) (41.7–44.2 MJ/kg), but its direct application in diesel engines is problematic. Engine trials show poor combustion, including long ignition delays, higher heat release rates, and significantly increased NOx, HC, and CO emissions, attributed to the high content of unsaturated alkenes and aromatics. Future work should focus on developing more robust catalysts, such as mesoporous zeolites, to ensure long-term stability. Finally, a deeper understanding of the complex synergistic mechanisms in co-pyrolysis and expanded system-wide LCAs are needed to fully optimize pyrolysis-based bio refineries.