There are slightly different strategy-options for different generations of the game. Most tips here work for every generation. This article works best for generation 4 and later released in 2006 and thereafter. The Legendary Pokémon are: Dialga, Palkia, Giratina, Shaymin, Uxie, Mesprit, Azelf, Arceus, Cresselia, Darkrai, Manaphy, Phione, Regigigas, Regice, Regirock, Registeel, Latias, Latios, Kyogre, Groudon, Jirachi, Deoxys, Rayquaza, Ho-oh, Lugia, Celebi, Raikou, Entei, Suicune, Moltres, Zapdos, Articuno, Mew, Reshiram, Zekrom, Mewtwo, Cobalion, Terrakion, Virizon, Keldeo, Meloetta, Victini, Genesect, Yveltal, Xerneas, Zygarde, Diancie, Hoopa, Volcanion, Cosmog who you get for free , Cosmoem evolves from Cosmog , Solgaleo, Lunala, Necrozma, Magearna, the next seven are Ultra Beasts Nihilego, Buzzwole, Pheromosa, Xurkitree, Kartana, Celesteela, Guzzlord, and Marshadow currently not available. Some of these Pokémon are mythicals, and tend to be given out in special events, instead of being captured. A waiting legend just sits and waits there for you Dialga, Palkia, etc. Roaming legends have you find them, then they run away Mesprit, Cresselia, Suicune, Raikou, Entei, etc. Item activated Pokémon requires an item from another game such as Wi-Fi connection, Mystery Gift, or hacking use only as a last resort , for example Shaymin, Heatran, Arceus, Manaphy, Deoxys, etc. Also, a select few legendaries or mythicals are given out for free, but you don't need to catch these, so if you're looking for one of those, you will not need this article's assistance. You can always find out information like this on the Internet. If it is a roaming legendary: use moves like Mean Look or an ability like Shadow Tag to ensure it can't escape! Shadow Tag and Mean Look can help out a lot! If you don't have a Pokémon with these moves, some legendaries will move to a new route every time you do, so switch between routes for a bit, and, if like in Pokémon HeartGold and SoulSilver you can see where the legendary is, you can tell when the legendary is near, and then go search for it. Know what level the Pokémon is, and the abilities and moveset it has. This is very crucial information. Knowing what type the legend is, helps determine what you will need to heal yourself Paralyze Heal, Awakening, Antidote, etc. Knowing the level will tell you what Pokémon to bring. Too low a level, and you will be defeated. Too high, and you defeat the legend. It is also a decent idea to bring a Pokémon to put your legend to sleep, as this improves your catch rates and gives you a few turns to heal, switch Pokémon, or throw Pokéballs. Save right before going into the battle. You may not get a second chance to catch it, and if you saved before you defeated it, you can soft reset L+R+Start+Select and try again! It is very comforting to have this save, and continuous soft resets can score you a shiny, although the chances are absurdly low. Use the right Poké Balls. It is generally a good idea to use at least Ultra Balls catch rate: x2. Use Net Balls for water and bug Pokémon catch rate: x3. You can use Dusk Balls at night day- and night-times are different for the Pokémon games. You should look that up on the internet. If you want even higher catch rates you can use Timer Balls the catch rate depends on the length of the fight: round 1-10: x1; round 11-20: x2; round 21-30: x3; round 31+: x4! Don't use the Master Ball unless you absolutely need to, because they are extremely rare! An unused Master Ball is a cool trophy! Every legendary CAN be caught in a Pokéball that isn't the Master Ball.