You have to walk around with it. It will hatch faster if you have a Pokemon with the ability Flame Body.
If you mean Flame Body, then only Magby and Slugma (along with their evolutions) have it.
use pokeradar on a body of water that has lots of gyrados
in almost every body of water (using surf)
Only Sableye has this Poke-Body. This card is 48/100 in Diamond and Pearl - Storm front.
after you beat elite4 and champ you have to get full pokedex to go to stark mountain and tons of slugma and macargos
Accually, it depends on what Pokemon you are trying to hatch, and it also depends on a Pokemon's abillity. If you have a Magmar or other Pokemon with the abillity Flame Body, eggs will hatch much faster.
some slugma have effect warm body it helps eggs hatch
You must have a Pokemon with magma armor or flame body the it should make the egg hatch 1/2 the time
By my opinion, no. Shellos is not a good Pokemon. Why is that? Because you catch it in very low levels, can be beat by ALL Grass-Type Pokemon and because it learns really bad moves (except Muddy Water and Body Slam). Hope I helped :)
In Pokemon Diamond Gyarados can be found in almost every body of water using the Super Rod. Alternatively you can catch a Magikarp and level it to 20 for it to evolve into a Gyarados.
I know it learns perish song, blizzard, body slam, and Ice beam. That is all I know