EDH

[Avodroc13]

If by some random chance, me and my opponent are both using the same commander, and we both manage to get them out, can I use {Act of Treason} and make both of them goto the graveyard? (or do they go back to the command zone to be cast again?)

[particle]

If by some random chance, me and my opponent are both using the same commander, and we both manage to get them out, can I use {Act of Treason} and make both of them goto the graveyard? (or do they go back to the command zone to be cast again?)

so technically, as a game of commander begins, each player reveals their general in turn order. however, once a general has been revealed to be played by a player, it cant legally be picked by another commander. in truth, however, edh is very casual so if your playgroup allows its fine.
now to answer your question.
first of all, no card of your opponents can ever go to your graveyard. even if your and your opponent are both playing {zedru, the great-hearted} and you each have mostly your opponents permanents under your control, a massive permanent wipe will still return all your cards to your graveyard and vice versa.
now, lets say you have any legendary creature and it happens to be the commander that your opponent was playing with. now you {act of treason} his commander. assuming it resolves, the legendary rule will trigger, and youll get to sacrifice your opponents general. however, once you do that, the general attempts to go to the OWNERS graveyard, and the owner gets to apply replacement effects like putting it in the command zone.

[Avodroc13]

Well done, Particle! Thanks for the detailed response.
I must find a zedru! :O That is a lovely card, that is!
I understand that My opponents' cards don't goto my graveyard, I was just wondering if the legend rule applies in EDH. I wasn't aware that people couldn't have the same commander.

[Remillo]

so technically, as a game of commander begins, each player reveals their general in turn order. however, once a general has been revealed to be played by a player, it cant legally be picked by another commander. in truth, however, edh is very casual so if your playgroup allows its fine.
now to answer your question.

Particle, I've never heard of a rule like that.  The only time when a rule like that may apply might be during League play where everyone 'claims' a General at the start of the League.  I'd love to know if that's written down anywhere.  I've certainly never seen it in the Comp Rules or the EDH Website.

[Double-O-Scotch]

I have to agree. I've never heard of any rule that prohibits using the same commander.

[Double-O-Scotch]

Must be.

[Avnger345]

League Rule: An EDH "League" consists of a regular group of players who frequently play together using the same decks. No two players in a league game may have the same General. Within a given league, Generals are allocated first-come, first-serve and are preserved between meetings/games. No player may have, in his or her deck, the General of any other player in the game; it should be replaced with some other card before the game begins. The 'Roll Call' forum provides a tool for organizing and publicizing EDH leagues and reserved Generals.

Open Play Rule: Open play EDH rules are used for games between opponents who do not routinely play together. Generals are not subject to the Legendary rule, although other creatures of the same name are; if a General and a non-General creature of the same name are in play, only the non-General is put into the graveyard by state-based effects. If two opponents in the same game have the same General and both are in play, neither is put into the graveyard. The General's mana cost limits what coloured mana symbols may appear on cards in the deck: if a coloured mana symbol is not present in the General's mana cost, the deck may not contain any cards using that mana symbol. Lands with a basic land type (basic lands, Shock lands, Dual lands, Shadowmoor CIPT-basics, etc) contain the corresponding mana symbol(s) as per CR 212.6g.

Example: If you were to play Phelddagrif (Casting cost 1UWG) as your General, your deck may not contain any red or black cards; no card in such a deck may contain red or black mana symbols or hybrid mana symbols (for example: Talisman of Dominance, Life//Death, and Boros Guildmage are not allowed).

A deck may not generate mana outside its colours; anything which would generate mana of an illegal colour generates colourless mana instead. An EDH deck must contain exactly 100 cards, including the General.

[Avnger345]

That last part yes.. That was from mtg wiki.. I'll edit that out of post