Pokemon Emerald ++ Legendary Pokemon Locations

------------------------ANY TIME------------------------

Regirock - Desert Ruins
Regice - Island Cave
Registeel - Ancient Tomb
Heatran - Mt Chimney
Regigigas - Sealed Chamber Inner Room (After collecting/defeating other 3 Regis)
Type: Null - Weather Institute
Silvally - Evolve Type: Null with friendship
Kyogre - Marine Cave
Groudon - Terra Cave
Rayquaza - Sky Pillar
Xerneas - Hidden Forest (Route 119 east side)
Yveltal - Magma Hideout 3F
Cosmog - Mt Pyre (multiple can be caught, 6F, Exterior, Summit)
Cosmoem - Evolve Cosmog
Solgaleo - Evolve Cosmoem during the day, lvl 53
Lunala - Evolve Cosmoem during the night, lvl 53
Phione - Underwater Route 127
Manaphy - Underwater Route 124
Victini - Fallarbor Town (Cozmos House, gift from the little girl)
Keldeo - Shoal Cave Low Tide Inner Room
Meloetta - Route 101 (east side after obtaining CUT)

-------------------AFTER OBTAINING NATIONAL DEX (BEATING THE GAME)-------------------

Articuno - Shoal Cave Low Tide Ice Room
Zapdos - New Mauville
Moltres - Fiery Path
Raikou, Entei, Suicune - Roaming (Track in your dex)
Latias - Roaming or Southern Island (Eon Ticket from your dad)
Latios - Roaming or Southern Island (Eon Ticket from your dad)
Cobalion, Terrakion, Virizion - Roaming (Track in dex)
Tapu Koko, Tapu Lele, Tapu Bulu, Tapu Fini - Cave of Trials (New cave on Route 107)
Lugia, Ho-Oh - Navel Rock (Mystic Ticket from Professor Birch)
Dialga, Palkia, Giratina - Space Temple (Mossdeep Space Center)
Reshiram, Zekrom - Artisan Cave
Marshadow - Hidden Forest (Route 119 east side after catching Xerneas)
Zygarde - Rusturf Tunnel
Mew - Faraway Island (Old Sea Map from rival's mom)
Shaymin - Petalburg Woods
Jirachi - May's Room at night
Deoxys - Birth Island (Aurora Ticket from your mom)
Genesect - Altering Cave
Diancie - Granite Cave (Steven's Room)
Magearna - Meteor Falls 1F
Zeraora - Scorched Slab
Meltan - Desert Underpass
Melmetal - Evolve Meltan lvl 45

------------------AFTER CATCHING MEW--------------------

Kyurem - Shoal Cave Low Tide Ice Room
Uxie, Mesprit, Azelf - Roaming (Track in your dex)
Cresselia - Dream Master's House (Slateport City, formerly Name Rater's House)
Tornadus, Thundurus, Landorus - Roaming (Track in dex)
Mewtwo - Pacifidlog Cave (top of Pacifidlog Town)
Celebi - Petalburg Woods (after catching Shaymin)
Darkrai - Dream Master's House (Slateport City, formerly Name Rater's House)
Arceus - Sky Pillar (after catching Rayquaza)
Volcanion - Mt Chimney (after catching Heatran)

----------------------HOOPA EVENT-----------------------

Hoopa can be found in Mirage Tower on Route 111. Upon first encountering it, it will flee from you. Portals containing the Ultra Beasts will be scattered across the region. Their locations are below. Once all Ultra Beasts have been caught, Hoopa will return to Mirage Tower for battle.

Nihilego - Route 129
Buzzwole - Route 103
Pheromosa - Route 110
Xurkitree - EverGrande City
Celesteela - Route 114
Kartana - Route 118
Guzzlord - Sootopolis City
Poipole - Route 109
Naganadel - Evolve Poipole
Stakataka - Route 115
Blacephalon - Route 132
Necrozma - Mt Pyre Summit

------------------NOTE ABOUT ROAMERS-------------------

Some roaming Pokemon are dependent on other roaming Pokemon being captured (only 6 can roam at a time). If you don't yet have the roaming trio that you want available for tracking in your Pokedex, catch the 3 that are available and then check again. The game is limited to 6 at any given time, so they are grouped as "post national dex" roamers and "post mew" roamers. Catch what is available then check your Pokedex for new entries.

------------------NOTE ABOUT SAME-SPACE LEGENDARIES-------------------

Some Legendary Pokemon can be found in the same map as other Legendary Pokemon. If you are looking for a particular Pokemon (for instance, Celebi) but another is in its place (Shaymin), catch that Legendary Pokemon, then leave and return to the area. As long as you meet the requirements (gained National Dex, caught Mew, etc.) then the other Legendary will appear.