What legendarys can you get(especally ho oh) and how do tou get them.?

All of the legendaries are obtainable. There are some you must obtain the friend area of first however. Ho-oh, Mew, Latios, Latias, Regirock, Regice, Registeel, Entei, Raikou, and Suicune all have purchasable friend areas that are needed to recruit them [all other legendaries give you their friend area with recruitment]. All of them, apart from Mew and Celebi, are simply waiting for you to come kick their tails in order to join you....Celebi, you simply get to the last floor in a certain dungeon where you are returned to Level 1, and it'll automatically join you. Mew, is one annoying cat. It appears randomly between floors 36 to 99 of Buried Ruins if you have a Music Box in your toolbox, so it takes a lot of time and luck, and don't worry about asking for help.....I've gone through that dungeon twice and still not even gotten a glimpse of Mew.

Hope I helped

You can get all of them. You have to beat the game first then go back and recruit them. Have to only tak one Pokemon I think they need two spaces

You can get them all but they are very hard to want to join you

Ho-Oh- You can access it by opening up the dungeon named Mt. Faraway.

Entei- Can gain access by either completing Stormy Sea or Solar Cave. (HM's needed from Solar Cave)

Rokiuo(Lightning Legendary dog can't remember name)- Can access by completing Fiery Relic. (Where Entei is)

Suicune- Can gain access by defeating Rokiuo, and going to the Northwind Field.

Lugia- By recruiting Moltres, Zapdos, and Articuno, you can access the Silver Trench, a 99 floor with Lugia at the end.

Zapdos- Defeat it numerous times and it will eventually join you. (Bring only 1 Pokemon)

Moltres- Defeat it numerous times and it will eventually join you. (Bring one Pokemon

Articuno- By defeating it numerous times, it will eventually join you. (Same as above)

Mew- After defeating all 3 Regi's, and gain the Music Box,it will randomly between floors 36-98.

Kyogre- Located at Stormy Sea floor 40, it will befriend you if you battle it 1-3 times.

Groudon- By defeating it after the storyline, it may join you. If not, just keep going and try to kill it.

Rayquaza- After getting Fly at Wyvern Hill, you can gain access to Sky Tower. Battle it numerous times, and it will join you.

Deoxys- *You have to find and kill Deoxys on each floor to get to floor 20* When you get to floor20, it might decide to join you after a couple battles.

Celebi- After getting on all 99 floors, it will simply ask to join you.

Mewtwo- Between 40-99 floors. You can gain access by defeating and recruiting Ho-Oh.

Latias & Latios- Asks to join you when you rescue Latias from the Pitfall dungeon.

You can get, as far as I know, Groudon, Kyogre, Zapdos, Moltres, Articuno, Deoxys, Celebi, Entei, Raiku, Suicune, Mew, Mewtwo, Rayquaza, Latios, Latias, Lugia and Ho-Oh. As for getting them, you must beat them in battle, but for some, you need a certain rescue rank.