Below there're the most used rules used here in the forum.
When you just say Standard rules, you're immediately agreeing with them when opening a thread.
* Sleep Clause
You can't use sleep inducing moves in opponent's Pokémon when there's another Pokémon in his/her team asleep. Yawn can't be used to PseudoHaze (make opponent switch) when there's another Pokémon asleep caused by you. When the asleep Pokémon awakes or faints, you're free to make another Pokémon of his/her team asleep. Sleeping being caused by Effect Spore or Rest are disconsidered from Sleep Clause.
* Species Clause
You can't use two of the same Pokémon in a team.
* Evasion Clause
You can't use moves that increases your evasion. Avoid the use of Acupressure, it has 1/7 chance to double your evasion.
* OHKO Clause
You are strictly prohibited of using OHKO moves. They are Guillotine, Horn Drill, Fissure and Sheer Cold.
* No Hacks
Don't need to explain, you are prohibited to use any illegally obtained Pokémon. Hacking parents to breed is also unaccepted, but people can't control this just looking at the stats.
* No Ubers
Uber Pokémon are overpowered Pokémon. Since these are "Standard Rules" you have to use the "Standard Pokémon". Click here for a list of Uber Pokémon
* No Hax Items
These are all the items that relies on luck to activate. These items are:
Brightpowder, Focus Band, King's Rock, Lax Incense, Quick Claw, Razor Claw, Razor Fang and Scope Lens. (Tell me if I missed some).
Note: Scope Lens and Razor Claw are considered Hax items, but they are the only one that is accepted normally in Wi-Fi.
* No Disconnecting
You can't turn off your
DS or move away from signal range to end a battle. People can have weak routers so don't always fight with the people if he/she disconnected.
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These are the rules that most people play, and below there're unusual rules usually applied, but it's outside of Standard:
* Self KO - NOT STANDARD!
You can't use Destiny Bond, Perish Song, Selfdestruct or Explosion to force a tie. People usually dislike the fact he/she lost the last Pokémon in a battle, the rule exists, but it's rarely added as standard since it's also a strategy.
* Item Clause - NOT STANDARD!
Two Pokémon can't hold same items. Using Trick/Switcheroo in a Pokémon and receiving/getting an item that other Pokémon in your team has doesn't break the clause.
* Freeze Clause - NOT STANDARD!
Pokémon can't Freeze two Pokémon at once.
Note: This clause is standard in battle simulators, since if one Pokémon is frost, the program can just ignore the freezing chance the attack has. But it's definately not standard since we never know if an attack is going to freeze.
* No Weather - NOT STANDARD!
It avoids the use of Hippowdon, Tyranitar and Abomasnow. Just because the battles slow down because of Sandstorm/Hail damage and leftovers recovery every turn.
* No SkarmBliss - NOT STANDARD!
A dumb rule created by someone unknown that didn't have skills to handle Skarmory and Blissey used in the same team. Definately not standard, but it's there... Also the combination of these aren't as effective as it was in Advance.
* No Legendaries - NOT STANDARD!
Another rule that avoids the use of Pokémon. The allowed legendaries are as strong as any OverUsed Pokémon, so they're completely fine in the standard play. BUT some people dislike them and decided to block all the legendaries. There's the Uber list to block the unfair legendaries (And Wobbuffet).
* No Baton Pass chains - NOT STANDARD!
Baton Pass chains are teams that uses a lot of Baton Pass Pokémon to get multiple boosts in a Pokémon.
* No switching - DEFINATELY NOT STANDARD!
People who are weak at predicting or just thinks switching is a waste of time, use this rule. Good luck at finding someone who agrees with this rule.
* Confusion Clause - NOT STANDARD!
No attacks that are sure to cause confusion can be used.
* Everything Goes - NOT STANDARD!
Self explanatory - No rules applied.
* Choice Clause - NOT STANDARD!
User can't use more than one Choice item in their teams (Choice Band, Choice Scarf and Choice Specs).