The best hint to geting the main pokemon is to keep the masterball that you get from Proffessor Rowan

Get all starters by trading You will need two game carts and two DS's for this not so cheap way of getting all three starters. Select a starter and trade it to the other game and star that game over. Do that until you get all the starters you want.

Sunnyshore Gym Leader

When you get to Sunnyshore CT go to the lighthouse and the gym leader is up the top. Go and beat him.

Catch Creselia or Mesprit

Make sure you got the map from the watchtower in Jubileaf City. Then you go to sand town right next to the Pokemon center on the right hand side. Up there will be a route. Keep on going in and out of the route and Creselia or Mesprite will keep on changing places. Eventually they'll be on top of you on the map. Go in to the grass and it will be there (MAP talk to the president by the counter).

Catch Heatran (in Stark Mountain)

To catch Heatran carry lots of duskballs.

Darkrai Well you have to have the cheat code to do it (run through anything). First go to Canalave City and go to sailor Eldercks house and talk to the kid. He will be talking about Darkrai. Then go outside and talk to sailer Elderck. He will take you to Fullmoon island and talk to Crecla then get the item then go out then run to the right then you will apear in New Moon Island. Talk to Darkrai. Be sure to save on Master Balls.

Level 100 Pokemon

An easy way to get your pokemon to level 100 is to keep fighting with the elite 4 at least 15 times.

Catch a Shaymin

First you must have the run/walk through anything cheat. Then you go through Victory Road on the right until you hit an area previosly blocked. Go through then walk up the route until you hit the rock with the dots on it. You go up in the water until you hit Seabreak Path. (Here's where I strongly suggest riding your bike.) You will come to a field of flowers. Talk to the Shaymin sitting in the middle. (If you also have the one hit kill cheat use it right as the Shaymin appears for an extra advantage.)

Union room glitch

Go to the union room then click a chat with your name on it. A red marker will be around you. Quickly exit and you will float away but the red marker will be still in the union room.

Tips to beat the Elite Four

First you will need a Polkia at Lv.90 tops. Make sure it knows the moves Flamethrower, Special Rend, Earth Power, and Slash. For the first person use Flamethrower on all of his pokemon. When you get to the second person use Earth Power on all of her pokemon. When you get to the thrid person use a mixture of all the moves except Special Rend, and if you have a Infornape use it. When you get to the thrid person use slash on all except Bronzong. Use Flamethrower on him. Now you are at the last person you will have to face before you are the champion. First she will use Spiritomb. Use Flamethrower on it. Then she will use Garchomp. Use Special Rend on it. Gastroodn is next. Use rock climb on it. Use the rest of your moves to defeat her.