With help of people in the thread, I tried a few things. Just waiting around will not make him reappear.
What will make Snorlax reappear in the bridge is to beat Elite 4. If you want it to appear again, simply go to Pokemon League and re beat the Elite 4.
This will apparently also work with other Pokemons like Mewtwo and Zapdos if you failed to catch them (thanks, scenia).
To expand a bit on what user2357112 mentions, your Pokémon raises its Affection by 'collecting' hearts. Each time you reach a certain threshold of hearts, your Pokémon will do a little animation (usually a dance or spin, but it varies from Pokémon to Pokémon), and a lot of hearts will come out from your Pokémon.
The number of hearts you need to collect for each level of affection are:
- Level 1 = 1 heart (Start)
- Level 2 = 50 hearts
- Level 3 = 100 hearts
- Level 4 = 150 hearts
- Level 5 = 250 hearts (Full Affection)
You gain hearts by petting & feeding your Pokémon. You can only pet and feed them so much in one turn however - once they stop giving hearts (and refuse food) you need to do something else.
The easiest method I've found is to alternate petting/feeding and playing the minigames. The steps are:
- Pet them until they don't give off hearts anymore
- Feed them until they eat slowly (they will refuse the next one)
- Play one minigame
- Repeat
Check out the Pokémon Amie page on Serebii for more info.
Side note: Affection is not the same thing as Happiness. Happiness is affected by walking, leveling up, fainting etc, It affects the power of the moves Return and Frustration, and is the method to which a lot of Pokemon evolve. Affection will make Eevee evolve into Sylveon, Happiness will make it evolve into Espeon (day) or Umbreon (night)
Best Answer
Yes -- more than one rotom will spawn, although they will always be in shaking trash cans. If you don't see any, try leaving and re-entering the area. In addition, they will only appear there on Tuesdays.