No you have to train surskit to level 22.
the Pokemon unobtainable are surskit, masquerain, zangoose, lunatone and Roselia
They are... Surskit, Masquerain, Meditite, Medicham, Roselia, Zangoose, and Lunatone
Taillow, Swablu, Gligar, Rayquaza, Trophius, Masquerain.
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 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.
Masquerain is a Bug and Flying type pokemon.
No you cannot catch Celebi in Pokemon Emerald.