You have to register certain people in your PokeGear and they will tell you of certain swarms happening. I also heard you can listen to the radio [Oak's Show] and he will say if a swarm is happening, [Random Swarm] but I only witnessed it in a video, which the player was in Kanto.
Once you have got the National Dex, go to Dawn's house in Sandagem Town. (Bottom Right below the Pokemon centre). Ask the little girl, Dawn's sister. She will say a route and tell you what Pokemon are swarming there. eg. route 228, Beldum. She willl also tell you, she wants you to be better than her sister Dawn. You can only do this once a day. Once you capture or battle the swarming pokemon, you will have to wait 24 hours to do another one. DO NOT CHANGE THE TIME or you'll have to wait longer.
Hope this helped!
http://www.serebii.net/platinum/swarms.shtml
You could find swarms of ralts on route 34 on the right day if you're lucky and then evolve it at level 20 or just trade for one somewhere
Aura Beam is in Pokemon HeartGold.
That is impossible in Pokemon HeartGold and SoulSilver.
No, you cannot sell eggs in Pokemon HeartGold.
You need to mate the Pokemon with a Ditto.
Unfortunately, there are no swarms on HeartGold and SoulSilver, only on Diamond, Pearl and Platinum.
You can catch them while they're in swarms. Otherwise it's almost impossible and will take you weeks non-stop. To get Pokemon in swarms you need to listen to the radio on your pokedex and wait for it to say where the snubull is swarming.
Ralts appear in 'swarms', you have to listen to the radio often until Mary announces breaking news where she will tell you were to go for ralts.
There is no best Pokemon on Pokemon HeartGold.
there is no Pokemon Mansion in Heartgold.
Snubull are usually found in swarms. Otherwise, they are really rare. Swarm locations and the Pokemon type can be found by listening to Professor Oak's and Mary's talk show on the radio.
They are not in Pokemon HeartGold
where is the pokemon transfer lab in heartgold
Route 14 swarms
swarms on route 222
They tell you where Pokemon are and where Pokemon swarms are.
You could find swarms of ralts on route 34 on the right day if you're lucky and then evolve it at level 20 or just trade for one somewhere