Emerald shares the same 386 roster as Ruby and Sapphire but changes availability. Some Pokemon show up earlier, others appear in new locations, and move tutors hand out coverage moves that aren't available in RS. Rayquaza is catchable at Sky Pillar before the Elite Four. Wallace is the Champion instead of Steven. Filter the Hoenn dex by type or stats to plan your team.
Slaking
Nincada
Ninjask
Shedinja
Whismur
Loudred
Exploud
Makuhita
Hariyama
Azurill
Nosepass
Skitty
Delcatty
Sableye
Mawile
Aron
Lairon
Aggron
Meditite
Medicham
Electrike
Manectric
Plusle
Minun
Volbeat
Illumise
Roselia
Gulpin
Swalot
Carvanha
Sharpedo
Wailmer
Wailord
Numel
Camerupt
Torkoal
Spoink
Grumpig
Spinda
Trapinch
Vibrava
Flygon
Cacnea
Cacturne
Swablu
Altaria
Zangoose
Seviper
386 across Gens 1 through 3. No new Pokemon over Ruby and Sapphire. Emerald's additions are about where things appear, not what exists. More wild encounters earlier, move tutors for coverage, and a few Pokemon in new locations. You still need to trade for version exclusives.
Both Team Aqua and Team Magma are antagonists (instead of one per version). Rayquaza is catchable at Sky Pillar before the Elite Four. Wallace is Champion instead of Steven. The Battle Frontier replaces the Battle Tower with 7 facilities. Move tutors teach coverage moves RS didn't have. And some wild Pokemon show up in new locations.
Yes. After the Groudon vs Kyogre showdown at Sootopolis, you go to Sky Pillar to summon Rayquaza. It flies off to stop the fight. Later, after getting the eighth badge, you can return to Sky Pillar and catch it. Level 70, 680 BST. It's one of the strongest Pokemon you can get before the credits.
Gen 3, GBA, 2004. Emerald is Hoenn's third version. The roster and ability system are the same as Ruby and Sapphire, but the story plays out differently (both villains active, Rayquaza resolves the conflict). The Battle Frontier postgame is the main draw for experienced players.
The Battle Frontier is Emerald's postgame challenge facility with 7 different battle formats: Battle Tower, Battle Factory, Battle Pike, Battle Dome, Battle Palace, Battle Arena, and Battle Pyramid. Each has a Frontier Brain boss. It's considered one of the hardest postgame challenges in any Pokemon game.
- Gen IY
Yellow151 Pokemon - Gen IRB

Red & Blue151 Pokemon - Gen IIGS

Gold & Silver251 Pokemon - Gen IIC
Crystal251 Pokemon - Gen IIIRS

Ruby & Sapphire386 Pokemon - Gen IIIFRLG

FireRed & LeafGreen386 Pokemon - Gen IIIE
Emerald386 Pokemon - Gen IVPt
Platinum493 Pokemon - Gen IVHGSS

HeartGold & SoulSilver493 Pokemon - Gen IVDP

Diamond & Pearl493 Pokemon - Gen VBW

Black & White649 Pokemon - Gen VB2W2

Black 2 & White 2649 Pokemon - Gen VIXY

X & Y721 Pokemon - Gen VIORAS

Omega Ruby & Alpha Sapphire721 Pokemon - Gen VIIUSUM

Ultra Sun & Ultra Moon807 Pokemon - Gen VIISM

Sun & Moon802 Pokemon - Gen VIILGPE

Let's Go Pikachu & Eevee153 Pokemon - Gen VIIISwSh

Sword & Shield664 Pokemon - Gen VIIIPLA
Legends: Arceus242 Pokemon - Gen VIIIBDSP

Brilliant Diamond & Shining Pearl493 Pokemon - Gen IXSV

Scarlet & Violet733 Pokemon - Gen IXLZA
Legends: Z-A364 Pokemon - Gen XWW

Winds & Waves51 Pokemon