Say I have an EDH/Commander deck with Omnath, Locus of Mana as my commander.
Does that count as being in my deck?
Or can I have another Omnath, Locus of Mana in my deck? (If so I imagine I would have to follow all the Legendary rules about playing the second one.)
If I could include a second one in my deck that could be useful (if the commander version gets killed a few times I would be able to play the one from the deck for only 3 mana.)
Yes, the Commander is part of the deck.
903.5a Each deck must contain exactly 100 cards, including its commander.
The Legend rule doesn't limit what can be present in a deck — it limits what's on the 'field — but the following Commander rule does:
903.5b Other than basic lands, each card in a Commander deck must have a different English name.
The uniqueness rule extends to the sideboard. You only have a single copy of a card in both the deck and 10 card sideboard combined.
No. The commander itself does not count as part of the deck. When you are playing EDH your Commander is technically off the board when it is in the command zone. So before you even start playing an EDH/Commander game the Commander is not in the deck. Ergo it does not count as part of your 100-card restriction.
