Location: Marine Cave

Method:
After completing the Elite Four, you will occasionally find strong weather on Routes 105, 125, 127 or 129. When the weather is in effect, you'll be able to gain access to the Legendary Pokémon Kyogre. It is at Level 70

Kyogre Level 70

OT: Yours ID: Yours Ability: Drizzle Hold Item: None

??? Nature. Date of Receiving Marine Cave. Caught at Lv. 70

Hydro Pump Rest Sheer Cold Double-Edge

Location: Terra Cave

Method:
After completing the Elite Four, you will occasionally find strong weather on Routes 105, 125, 127 or 129. When the weather is in effect, you'll be able to gain access to the Legendary Pokémon Groudon. It is at Level 70

Groudon Level 70

OT: Yours ID: Yours Ability: Drought Hold Item: None

??? Nature. Date of Receiving Terra Cave. Caught at Lv. 70

Rest Fissure Solar Beam Eruption

Location: Desert Tomb

Method:
This generation's legendary trio has a bit more legwork involved with obtaining. Before the three locations become available to you you must have a Relicanth and Wailord as well as a Pokemon with Dig and Dive. On Route 134 you must take the correct path through the currents to the patch of water you can Dive in. Once below folow the path up to the Braille inscription and resurface. Go to the next inscription and use Dig. Make Wailord the 1st of your party and Relicanth the 6th, then read that inscription. Three earthquakes will trigger and open passages on each respective route.
Regirock is found in the Desert Tomb, which is at the bottom of the sandstormy desert in Route 111. Scribed on the walls inside is a message like the ones on Route 134: go left twice, down twice and then use Rock Smash and the door to Regirock should appear. It's at Level 40, so be prepared.

Regirock Level 40

OT: Yours ID: Yours Ability: Clear Body Hold Item: None

??? Nature. Date of Receiving Desert Tomb. Caught at Lv. 40

Superpower Ancientpower Curse Rock Throw

Location: Island Cave

Method:
This generation's legendary trio has a bit more legwork involved with obtaining. Before the three locations become available to you you must have a Relicanth and Wailord as well as a Pokemon with Dig and Dive. On Route 134 you must take the correct path through the currents to the patch of water you can Dive in. Once below folow the path up to the Braille inscription and resurface. Go to the next inscription and use Dig. Make Wailord the 1st of your party and Relicanth the 6th, then read that inscription. Three earthquakes will trigger and open passages on each respective route.
Regice is hiding out in Island Cave, which is on a small reef on Route 105. Once inside, you will find a message in braille telling you to lap the cave twice clockwise, staying by the wall. Another Level 40 Pokemon, you should avoid its Icy Wind move.

Regice Level 40

OT: Yours ID: Yours Ability: Clear Body Hold Item: None

??? Nature. Date of Receiving Island Cave. Caught at Lv. 40

Superpower Ancientpower Curse Icy Wind

Location: Ancient Tomb

Method:
This generation's legendary trio has a bit more legwork involved with obtaining. Before the three locations become available to you you must have a Relicanth and Wailord as well as a Pokemon with Dig and Dive. On Route 134 you must take the correct path through the currents to the patch of water you can Dive in. Once below folow the path up to the Braille inscription and resurface. Go to the next inscription and use Dig. Make Wailord the 1st of your party and Relicanth the 6th, then read that inscription. Three earthquakes will trigger and open passages on each respective route.
Registeel is the last of the three, found west of Lilycove in Route 120's Ancient Tomb. The answer to this riddle to is use Flash in the middle of the room. Doing so will expose Registeel. This one is at Level 40 as well.

Registeel Level 40

OT: Yours ID: Yours Ability: Clear Body Hold Item: None

??? Nature. Date of Receiving Ancient Tomb. Caught at Lv. 40

Superpower Ancientpower Curse Metal Claw

Location: Sky Pillar

Method:
High above Sky Pillar after you earn the title of Champion waits Rayquaza, who instantly negates all weather in battle and has a mighty line up of moves. Two strong and useful STABS, a recovery move, and a priority attack make for a battle that demands only your best. It can Rest off status, remember, so bright a couple dozen of your favourite Pokeballs and a well planned team.

Rayquaza Level 70

OT: Yours ID: Yours Ability: Air Lock Hold Item: None

??? Nature. Date of Receiving Sky Pillar. Caught at Lv. 70

Fly Rest Outrage Extremespeed

Location: Southern Island

Method:
after choosing which Pokémon you saw on the TV after beating the Elite Four, the other will be available elsewhere. They can be found on the Southern Island if the player obtains an Eon Ticket through an e-Reader card (distributed through Nintendo Power) or by mixing records with someone who has it. Norman, your father, will give you the ticket and tell you to visit Lilycove City where Mr. Briney will ferry you to the secret island. There you can find the legendary dragons at a higher level in a secret forest. Be careful though as it has some strong moves and is holding a Soul Dew, which increases its Special Attack and Special Defense.

Latias Level 50

OT: Yours ID: Yours Ability: Levitate Hold Item: Soul Dew

??? Nature. Date of Receiving Southern Island. Caught at Lv. 50

Mist Ball Psychic Recover Charm

Latios Level 50

OT: Yours ID: Yours Ability: Levitate Hold Item: Soul Dew

??? Nature. Date of Receiving Southern Island. Caught at Lv. 50

Luster Purge Psychic Recover Dragon Dance

Method:
After you beat the Pokemon League, these Pokemon roam around Hoenn in the fashion of the Legendary Dogs from Gold and Silver. They flee the first turn and appear elsewhere on the map. You must trap them with a move like Spider Web to have a proper fight. After seeing the TV, you'll be asked what colour the Pokémon was and that will determine which one roams. The former is more offensive oriented, and the latter is more defensive, so choose your Pokemon for battle accordingly.

Latias Level 40

OT: Yours ID: Yours Ability: Levitate Hold Item: None

??? Nature. Date of Receiving ??. Caught at Lv. 40

Water Sport Psychic Refresh Mist Ball

Latios Level 40

OT: Yours ID: Yours Ability: Levitate Hold Item: None

??? Nature. Date of Receiving ??. Caught at Lv. 40

Water Sport Psychic Refresh Luster Purge

Location: Faraway Island

Method:
Exclusive to Pokémon Emerald is the ability to find Mew. If you get the Old Sea Map, you will be able to go to the Faraway Island. When you go inside, you will see Mew in a forest area and it will run away. Chase it down and you will be able to battle and catch Mew

Mew Level 30

OT: Yours ID: Yours Ability: Ssynchronize Hold Item: None

??? Nature. Date of Receiving Faraway Island. Caught at Lv. 70

Pound Transform Mega Punch Metronome

Location: Navel Rock

Method:
The legendary birds of the Johto region take residence in the eighth Sevii Island, Navel Rock. To get there, you need the MysticTicket. Inside the island there are two paths; the one on the left takes you up a long flight of stairs to meet Ho-oh at the summit, whereas the one on the right takes you down to the heart of the island underwater to meet Lugia. Be prepared for a tough battle - both are at Level 70.

Lugia Level 70

OT: Yours ID: Yours Ability: Pressure Hold Item: None

??? Nature. Date of Receiving Navel Rock. Caught at Lv. 70

Recover Hydro Pump Rain Dance Swift

Location: Navel Rock

Method:
The legendary birds of the Johto region take residence in the eighth Sevii Island, Navel Rock. To get there, you need the MysticTicket. Inside the island there are two paths; the one on the left takes you up a long flight of stairs to meet Ho-oh at the summit, whereas the one on the right takes you down to the heart of the island underwater to meet Lugia. Be prepared for a tough battle - both are at Level 70. Once you capture Ho-oh, don't forget the Sacred Ash that lay hidden where it was standing.

Ho-Oh Level 70

OT: Yours ID: Yours Ability: Pressure Hold Item: None

??? Nature. Date of Receiving Navel Rock. Caught at Lv. 70

Recover Fire Blast Sunny Day Swift

Location: Birth Island

Method:
For the first time ever you can catch the final Pokemon of the Hoenn Pokedex, Deoxys, provided you've got the AuroraTicket item. Deoxys is fittingly found on the last Sevii Island, Birth Island - but only after you complete a rather unique puzzle. This puzzle involves chasing a black triangle around the island and talking to it until it becomes red hot, after which Deoxys will emerge and attack. Perhaps unusually, Deoxys is the lowest leveled Legendary Pokemon at just Level 30, so be careful not to knock it out.

After you catch Deoxys it will revert to Speed Forme. These cannot be changed without trading, and only then as long as the Pokemon is in the game - however, stats will still be calculated accordingly for link battles. That is to say, for example, that a Deoxys on Emerald would have its Speed Forme stats when fighting against FireRed (and vice versa).

Deoxys Level 30

OT: Yours ID: Yours Ability: Pressure Hold Item: None

??? Nature. Date of Receiving Birth Island. Caught at Lv. 30

Knock Off Pursuit Psychic Swift