This should be a straightforward route. In the patch of long grass, there is a man hiding in the trees who will give you two Nuggets if you talk with him twice. Also, one of the Trainers is also hidden. You will need Cut for finding two of the items. In the southernmost area where two of the Trainers are, there are two paths. Going west will take you to Route 230, while going east takes you to the Resort Area. Let's go to the Resort Area first.
There isn't much to do here. This is the only place in the game besides Twinleaf Town not to have a Poké Mart or other store.
The Ribbon Syndicate is the large building in the northeastern part of town. This is a very hard building to get into as you must have 10 different kinds of Ribbon on your current party just to be permitted entry. You'll need to participate in a lot of different Super Contests to achieve this.
Like with the massage therapist in Veilstone City, there is a spa treatment, receivable once per day, that will increase a Pokémon's happiness factor. One difference is that it can also be used on Pokémon Eggs, enabling the Pokémon that hatches from that Egg to already possess that increased happiness factor. Also, you can purchase rare, highly expensive Ribbons not found elsewhere.
For the last numbered route in the game, this is pretty easy to navigate. Surf west to reach the Fight Area. If you have a Grass- and an Electric-type with you, you should have no problems. You will need Rock Smash for the small island found on this route to reach all the items (two of which are hidden).
When you approach the temple, the guard states that you are not qualified to enter, but Candice appears and says that you are.
Snowpoint Temple 1F
Travel down the stairs to B1F.
Snowpoint Temple B1F
Carefully slide down the ice and reach the stairs to B2F.
Snowpoint Temple B2F
Rock Smash can help here, although you do not actually need it to get through. After following the path, take the stairs to B3F.
Snowpoint Temple B3F
Sliding on the ice is a bit tricky. First, slide until you got to the part where there is no ice. Next slide ←, ↑, →, then ↑ to reach the stairs. You can now go to B4F.
Snowpoint Temple B4F
While there is nothing to worry about you can use Strength and move the boulder ↑, →, → to be able to reach the item. When ready use the stairs to descend to BF5, the final floor.
Snowpoint Temple B5F
While this new sliding puzzle looks difficult, it can be easy with the right steps. From the tile next to the first rock nearest your entry point travel ↓ to reach the unfrozen tile southwest of Regigigas. Now very carefully slide in this order: ↓, →, ↑, ←, ↓, →, ↑ to reach Regigigas. If you have the three Regis in your party, Regigigas will awaken and face you when you interact with it. Save the game before interacting with it.
It may come as a bit of a shock that Regigigas is only Level 1! Use False Swipe to reduce its HP bar to the red zone and then throw Dusk Balls or Nest Balls until you catch it. Hopefully, it won't be too much trouble.
Backtrack your way to the area where you were first outside in the summit earlier. (See this section for a refresher on how to get there.) Then, use the eastern entrance to the part of Mt. Coronet 4F below the waterfall. Climb the waterfall and go inside the cave to find the Adamant Orb and the Lustrous Orb (as well as the hidden Stone Plate). You will need both Orbs to catch Dialga and Palkia.
If you return to the tunnel, since Team Galactic is gone now, you can go through the door that was previously inaccessible. That will take you to Mt. Coronet's north area, where you can find TM02 (Dragon Claw) (as well as the hidden Nugget on the rock just north of it).
Here, you'll see a blue dimensional rift which is another dimension where Dialga is. Save your game, then interact with it to challenge Dialga. After that, step back inside Mt. Coronet and quickly return. This time, a purple-colored rift will appear: Palkia.
When you face them, be careful as they are at Lv. 70. Make sure your team is at least Lv. 65 or higher. Weaken them with normally-effective moves and inflict either paralysis or sleep. They have Earth Power to counter Steel-types that could withstand their other moves, but certain Steel-types like Skarmory or Bronzong still work for the resistance tactic as their additional types (or ability) prevent supereffective damage. Additionally, Shedinja is immune to all their moves.
Net Balls will make it easier to catch Palkia, as it is part Water-type. When playing at night, Dusk Balls will work great on both Legendaries.
After catching the deities of space and time, your mission in this game is mostly complete! All that's left is to work on completing the National Pokédex, which will require trading with other players. Obtaining all 481 non-event Pokémon is a big task, but it is possible! If you complete the National Pokédex, go to the Hotel Grand Lake on Valor Lakefront and talk with the Game Freak director to get your Diploma for completing your Pokédex.