There are quite a few moves that can make your opponent fall asleep:
Hypnosis - 60% Accuracy - Psychic
Dark Void - 80% Accuracy - Dark
Grasswhistle - 55% Accuracy - Grass
Lovely Kiss - 75% Accuracy - Normal
Sing - 55% Accuracy - Normal
Sleep Powder - 75% Accuracy - Grass
Spore - 100% Accuracy - Grass
Yawn - '--' Accuracy - Normal - (At the end of the turn after using Yawn, the target falls Asleep unless it is switched out.)
Courtesy of Pokemon.Marriland.com
------
If you're doing the Pokemon Leaf puzzle on Pokemon.com, then the answer would be spore.
Chat with our AI personalities
It makes your opponent's pokemon's speed sharply fall
I only know 3 moves that makes Pokemon fall asleep. GrassWhistle - Roselia learns it by level up Yawn - Dunsparce learns it by level up Hypnosis - Drowsee knows it when captured in Pokemon Heart gold And Soul silver.
There is no TM "Drowsy" in any Pokemon games. You maybe thinking of the move "Yawn" that makes the target drowsy in one turn, and makes them fall asleep the next. However, this move is not available via TM or Move Tutor either. There is a Pokemon named Drowzee also.
Sadly, Porygon is unable to receive a move that can put the opponent to sleep. He can however learn the moves Lock onand Zap Cannon. This combo allows Porygon to ensure paralysis while landing a solid electric type move.
When its tired. LOLOLOOLOLLOLOLOLOLOLOLOLOLOLOLOLOLOLOLOLOLOLOLOLOLOLOLOLOOOOOOLLLLLLOLOLOLOLOLOLOLOLOLLLOLLOLLOLOLLOLOLOLOLOLOLOOLOLOLOLOLOLOLOLOOOOOOOOOL!!!!!!!!!!!!!!!!!!!!!!!!! ZOMFG OWNED!!!!!!!!!!!!!!!!!!!!! LULULULULULULULULULULULULULULULZZZZZZ!!!!!!!!!!!!!!