Evolve Magikarp at lv20, or if you're luck, you can find some at Sootopolis City, use Super Rod.
you cant, but there is only 20% chance to catch him.
Yes, You can catch Groudon in Pokemon Emerald.
You can't catch one in Pokemon Emerald.
No you cannot catch Entei in Pokemon Emerald.
You can't catch a Bellsprot in Pokemon Emerald. You trade it from Pokemon Leafgreen!
There are many Pokemon you catch that are similar in sapphire and emerald but there are many Pokemon emerald can only get and not sapphire.
you dont need to find them you have to fight(and is best to catch) the red garydos on the lake. you dont need to find them you have to fight(and is best to catch) the red garydos on the lake.
You can't catch or obtain other trainers Pokemon in emerald.
Cressilia is a 4th generation Pokemon so you can't catch it in Pokemon Emerald.
No you cannot catch Celebi in Pokemon Emerald.
you cant. You can only catch it in Pokemon emerald, but, you cant catch latias in emerald.
You can onl catch LUNATONE in SAPPHIRE but you can catch solrock in emerald