Game Boy screens (DMG, Pocket, Color, Advance) have a **plastic lens/protector** over the actual LCD. Marker ink sits on this plastic—**not inside the liquid crystal layer**. It can usually be removed.
If the marker bled *under* the plastic protector (visible at extreme angles), **you cannot clean it without disassembly**. Options:
Pro Tip: After cleaning, apply a **matte screen protector** (e.g., Hori, generic cut-to-fit). Protects against future marks and reduces glare.