You will rescue the invisible Pac-Man on level 7. He has the ability to pass through ghosts unharmed. Use him to eat pellets that in dangerous locations.
Refill Lives Cheat
You can get full lives in PAC-MAN Friends by changing your phone's time setting. Close your PAC-MAN Friends. Set your time in advance for one day above. Open the game and you will get your full lives.
Scoring
Although the small pellets are only worth 10 points each, if you eat them consecutively each one will be worth more. You will lose this bonus though if you take too long to eat the next pellet.