What is Oathbreaker?
It is a causal multiplayer format that emphasizes the power of Planeswalkers. It provides players with new and interesting deck building challenges in a faster format. Decks are made of 60 cards, including an Oathbreaker and a Signature Spell. You can fine out more by checking out the quick rules, the comp rules, and the homepage.
Some Planeswalkers took oaths to protect the people of the multiverse. In order to fight each other, they might have to break these oaths.
Besides, it's a catchy name.
Who created Oathbreaker?
Why is the deck limit 60 cards?
This encourages focused deck building. It encourages themed deck-building. It forces players to make hard cuts. Wizards (usually) designs cards with a 60 card library in mind.
If you insist on playing with 100 cards, we won't stop you. We encourage you to refer to such games as "Oathbreaker100".
Why 20 life?
This, combined with the 60 card deck limit, allows for games to be about 30-60 minutes. The life total accounts for the fact that your Oathbreaker will likely absorb quite a bit of damage over the course of the game.
Can Oathbreaker be played one-on-one?
This is intended to be a casual multiplayer format. We encourage people to have fun, not be too competitive, and try to be creative with themes and unique ideas.
What about mulligans and drawing on the first turn?
In Oathbreaker, just like in other multiplayer games of Magic, each player gets a free mulligan and every player (even the first one) draws on their first turn. As of July, Oathbreaker will use the London Mulligan.
What is a Signature Spell?
The Signature Spell is an instant or sorcery spell within your Oathbreaker's color identity. It lives in the command zone. You are only able to cast it if your Oathbreaker is on the battlefield under your control. It is also subject to "command zone tax."
Can my Signature Spell be shuffled into my library?
The signature spell only has two places it can exist: the stack and the command zone. If it would somehow go to any other zone, it returns to the command zone instead. This supersedes any other replacement effect.
How do spells with alternative costs work as signature spells?
The "commander tax" is an additional cost. It has to be paid, no matter how you cast the spell. For example, if your signature spell is Force of Negation, you will either pay 1UU and the command tax or you will exile a blue card from your hand and pay the command tax. The second time you cast the spell, it will cost 3UU or exiling a blue card+2.
Affinity and Trinisphere and Command Zone Tax, oh my!
To calculate the cost of your Signature Spell (or Oathbreaker), use this formula: [The spell's printed cost OR alternative cost] + [additional cost (e.g., Thalia, command zone tax)] - [reducers (e.g., affinity)]. Finally, apply Trinisphere
Can I use a transforming Planeswalker as my Oathbreaker?
The Oathbreaker must be a Planeswalker on its front side. Arlinn Kord could be your Oathbreaker. Jace, Vryn's Prodigy could not.
Does my Signature Spell have to match my Oathbreaker's color identity?
It doesn't have to contain all colors of your Oathbreaker, but it must fall within the color identity. For example, you could play a red spell with a blue/red Oathbreaker.
Can I put cards with the "Devoid" mechanic in my colorless Oathbreaker deck?
No, you cannot. "Color" is not the same thing as "color identity". The color identity of a devoid card is still based on its mana cost and other mana symbols found on the card that are not in any reminder text surrounded by parenthesis. The color of a card is based on the color in the mana cost of the spell or any other color indicators on the card. For example Bearer of Silence  is a colorless card but its color identity is black.
Can I play cards with the "Devoid" mechanic if my Oathbreaker doesn't share a color in their mana cost?
No. See answer to previous question.
Is there a sideboard?
Not officially. Your Burning Wish looks lonely.
What about cards that say "your commander"?
Cards that reference "your commander" instead reference "your Oathbreaker." This wasn't an easy decision to come to. In the end, it didn't make sense to eliminate such cards from the card pool.
Can I have Partner Oathbreakers?
You can. Each Planeswalker has their own color identity, and therefore, their own Signature Spell. This means that you will have 4 cards in your Command Zone (and only 56 in your library). You may only cast the Signature Spell of the Oathbreaker currently on the battlefield and under your control.
Can I use a split card as my Signature Spell?
Yes! Remember that the color identity of the split card includes the casting cost of both sides of the card. The "command zone tax" is calculated based on the number of times the card has been cast. It doesn't view each side separately .