As long as Snorlax is Asleep, your opponent's Active Pokémon can't retreat.

Toss and Turn

20+

If Snorlax is Asleep, this attack does 20 damage plus 30 more damage. (This attack can be used even if Snorlax is Asleep.)

Heavy Press

40+

Flip a coin. If heads, this attack does 40 damage plus 40 more damage. If tails, Snorlax is now Asleep.