No to get Cyndaquil you must catch all Pokemon from that region, because if you have to catch every single Pokemon, won't you already have Cyndaquil?
You can't catch one in Pokemon Emerald.
Yes, You can catch Groudon in Pokemon Emerald.
You need to trade from every game.
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.
Cressilia is a 4th generation Pokemon so you can't catch it in Pokemon Emerald.
You can't catch or obtain other trainers Pokemon in 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.
hay even people how just started the game know all you have to have is oke balls AND YOU CATCH EVERY POKEMON YOU SEE AND YOU DONT HAVE that's how you catch every Pokemon