The mēng reading (level tone) is the colloquial / spoken cluster — sneakier and more conversational than méng. Three uses: (1) to cheat —
蒙骗 (hoodwink),
瞎蒙 ('blind-cheat'), the casual
你别蒙我 ('don't bullshit me'); (2) to guess —
蒙对了 /
蒙答案 (guess the answer when you don't know it); (3) to be dazed / knocked-out —
发蒙 (be confused, blanking out),
蒙蒙亮 (first dim glimmer of dawn — 'still in a daze').