Players may only use Pokémon HeartGold Version or Pokémon SoulSilver Version Game Cards.

Players at European events may only use European versions
Players at United States events may only use North American versions
Players at the World Championships may use any version
Players must provide their own Nintendo DSâ„¢ system Game Card and cannot share Game Cards with another player at the event.

Players compete in one of two age divisions based on their date of birth.

Junior Division: Born in 1998 or later
Senior Division: Born in 1997 or earlier

All event registration will be handled on-site. During registration, each player will be required to fill out a Team Information Sheet.

Each player must enter 4-6 Pokémon on his or her Team Information Sheet. See the Ineligible and Restricted Pokémon lists below for more information on which Pokémon are eligible for the tournament.
Each player must enter 0-6 held items on his or her Team Information Sheet.
Players may only use Pokémon and held items listed on their Team Information Sheet during the tournament.
The Pokémon and held items listed on a player's Team Information Sheet may not be changed once the player has registered for the event.
Players may change which held item a Pokémon is using between matches so long as both the Pokémon and the held item are listed on the player's Team Information Sheet.

Each match is played using the Pokémon Communication Club Coliseum, found on the top floor of the Pokémon Center in Pokémon HeartGold and Pokémon SoulSilver Versions. The tournament will use the GS Cup rules set, with some additional restrictions.

Each player uses four Pokémon during the battle, and sends out two Pokémon at a time.
The Flat Battle rules have an auto-level feature, which sets all Pokémon that are above level 50 down to level 50 for the duration of the battle with the following parameters:

Each Pokémon retains all of the moves that it knew before being auto-leveled
Pokémon that evolve after level 50 do not devolve when auto-leveled
Pokémon below level 50 remain at their actual level rather than being auto-leveled up to level 50 for the battle
The Pokémon's stats are adjusted to what its level 50 stats would be
A player's team may not contain two Pokémon with the same National Pokédex number.
Each Pokémon on a player's team may use held items, though no two Pokémon may hold the same item during battle. Allowed items include held items from Pokémon HeartGold and SoulSilver Versions as well as from earlier video games, including Berries 1-64. The Soul Dew item may not be used.
Players may not enter two Pokémon with the same nickname.
Players may not enter a Pokémon nicknamed with the name of another Pokémon character (for example, a Lucario nicknamed "Spiritomb".
Players found to have inappropriate/offensive Trainer names or Pokémon nicknames, as determined by the event staff, will be disqualified from the event.

Players may use Pokémon found in the Pokémon HeartGold and Pokémon SoulSilver Versions National Pokédex, from 001 to 493, including those Pokémon imported from earlier video games, with the exception of the Pokémon listed below.

Ineligible Pokémon
The following Pokémon NOT eligible for use in the tournament:

151 - Mew
251 - Celebi
385 - Jirachi
386 - Deoxys
489 - Phione
490 - Manaphy
491 - Darkrai
492 - Shaymin
493 - Arceus

Restricted Pokémon
During battle, a player's team of four Pokémon may not have more than two Pokémon from the list below. A player's Team Information Sheet may contain up to four Pokémon from the list below, as long as two non-restricted Pokémon are also listed on the sheet.

150 - Mewtwo
249 - Lugia
250 - Ho-Oh
382 - Kyogre
383 - Groudon
384 - Rayquaza
483 - Dialga
484 - Palkia
487 - Giratina

Move Restrictions
Pokémon may only use moves (including those learned in an earlier video game) that have been learned through one of the following methods:

By leveling up
By TM or HM
As an Egg move, through breeding
From a Move Tutor
Already learned by a Pokémon that was received at an official Pokémon event or promotion
Already learned by a Pokémon that was received from another Pokémon game (such as the Pikachu that knows Surf from Pokémon Battle Revolution)
By Smeargle's "Sketch" move (limited to the above moves learned by Pokémon from 001 to 493)

The use of external devices to alter the Pokémon in a player's party is expressly forbidden. Random checks will be performed throughout the tournament to determine whether or not an external device has been used to modify a player's party. Players found to have Pokémon that have been tampered with will be disqualified from the event, regardless of whether the player tampered with his or her game or received a Pokémon or item that was tampered with by someone other than the player. It is the player's responsibility to have legal Pokémon. Event officials have the final determination regarding the legality of a Pokémon.

A player should notify the staff immediately if he or she believes that there is a problem with an opponent's Pokémon. At the end of the round, all match results become final. Issues that go unreported until after the round has completed will not change the result of that match, regardless of whether there is a problem with an opponent's Pokémon.

Players and spectators are expected to demonstrate proper sportsmanship over the course of the event. A player may be disqualified from the event based on actions taken by friends or relatives who disrupt the operation of the tournament.

I do not own this, this was copy and pasted from from the following.

http://www.pokemonvgc.com/en/regulations.php

You can go there to learn more, also I don't know for sure if you can still enter. These are the rules I play by, I'm udjusting my team as of now to meet these regulations.

ATTENTION: I will host tournaments every now and then using these rules.

RoD