Partner

Partner is a keyword ability specifically used in the Commander format. Partner was introduced in Commander 2016. The Partner with variation allows only a specified other card to be the partner, but also allows a player such as a Two-Headed Giant teammate to tutor for the other card. 
==Description==
A player can have two commanders if both have partner. Because both commanders start the game in the command zone, the remaining library is only 98 cards. Your two commanders are treated individually for all other Commander rules. If either leaves the battlefield, you can return it to the command zone instead. The "commander tax", the additional cost of 2 for every time you've cast a commander from the command zone, applies individually. Combat damage dealt by each commander is similarly tracked individually. If either commander can deal 21 or more combat damage to a single player over the course of the game, that player loses.
If any card refers to your commander (or commanders in general), it means either one of the two. 
Partner was heavily featured in Commander Legends, where it appeared on 40 monocolored (and one colorless) legendary creatures and planeswalkers.
Note that while the Partner ability does not explicitly prohibit a card from being partners with itself, the singleton rule of Commander formats prevents it nonetheless.
===Partner with===
This variant is relevant in both commander and non-commander formats, and was introduced in Battlebond for Two-Headed Giant. It only allows one specified other card to be a co-commander, but as an alternative to that usage, it also allows a player to search their library for the partnered card and put it in their hand (aka tutoring). Cards with "partner with" always appear alongside their counterpart in booster packs, even for rare partner pairs.
When the partners in a pair are not legendary, they cannot be commanders, so the tutoring effect is the relevant one. They could be included in the same non-commander deck, or a commander deck whose color identity includes both partners. They could also be split across two teammates' decks in a format such as Two-Headed Giant. Battlebond has an uncommon cycle of non-legendary enemy-color partner pairs.
When both partners in a pair are legendary, all the non-commander play patterns are still possible, but the cards can be commanders as well. The co-commander option is one possibility, or one of the cards could be a commander which allows a teammate to tutor for the partner. Battlebond includes a rare cycle of legendary enemy-color partner pairs, as well as a mythic pair of planeswalkers (Will and Rowan). Commander 2020 included a rare cycle of wedge pairs, each with a monocolor human bonder of the common enemy color to its allied-color non-human partner. The "Heads I Win, Tails You Lose" Secret Lair drop included reprints of the rare pair from Battlebond, and the Innistrad: Crimson Vow Commander decks included two ally-color pairs ( and ) for the first time.
Certain Universes Beyond products include partner with pairs as well. Jurassic World Collection includes a pair, Doctor Who includes a pair and a pair, Tales of Middle-Earth includes a pair and a pair, and Assassin's Creed includes a pair.
While the rules allow for one of the cards to be a commander and the other to be a regular part of the same deck (and therefore tutor-able by the commander), as of Crimson Vow no partner pairs have been printed in which one has a subset color identity to the other. This makes it impossible to include both partners in the same commander deck this way due to color restrictions. Similarly, no partner pairs been printed in which one is legendary (and thus a possible commander) and the other is not.
It should be noted that the Unified Deck Construction rules for team formats prevent teammates from having copies of the same card in both decks, making it impossible to fully exploit both uses of "Partner with" at the same time: If both partners are co-commanders, then the counterpart to one of them is already in the same deck, and therefore cannot be present in a teammate's deck to be tutored for. Theoretically, a player could target an enemy player to allow them to tutor for the partner, which could be relevant for temporary alliances in a Free-for-All game. A player could also target themselves or a teammate simply to allow them to shuffle their library after "failing to find" the partner.
===Legendary partner===
The non-legal Heroes of the Realm card <c>Sol, Advocate Eternal</c> experimented with legendary partner: (You can have two commanders if [this] is one of them. The other one is promoted to legendary.)
==Variants==
It became apparent during the play design of Commander Legends that the partner mechanic had a limitation. Open-ended partner would limit what R&D could make legendary in the future.
Partner-like mechanics need to be self-contained as they grow in power pretty fast when you add things. Every partner you add to the game powers up every existing creature with partner, and there just comes a limit where the mechanic will break (aka be too powerful where many cards with partner would need to be banned). The future of Partner is mostly going to be partnering with specific subsets. Mark Rosewater doesn't think that R&D can make many more generic partner cards.
Battlebond already created a workaround with the "partner with" mechanic. Those cards can partner, but only specifically with one other creature. Other variant followed later.
===Friends forever===
A renamed Partner appeared in Secret Lair Drop Series: Stranger Things as "Friends forever". Partner and Friends forever are not compatible. Seven Legendary creatures were printed with this variant.
===Choose a Background===
Battle for Baldur's Gate created yet another take on Partner with Backgrounds named "Choose a Background". Backgrounds are legendary enchantments that exclusively grant Commanders abilities, limiting their independent utility. Thirty Backgrounds were printed with thirty-two legendary creatures that can choose them.
===Doctor's Companion===
The non-canon Doctor Who set introduced Doctor's Companion. Rather than a single legendary creature card, you may designate two legendary creature cards as your commander if one of them has the Doctor's Companion ability and the other is "the Doctor": this is defined as a creature having the typeline "Time Lord Doctor" and no others.
One card, <c>Amy Pond</c>, has both mechanics: Doctor's Companion, and Partner with <c>Rory Williams</c>. The release notes state that Amy must choose one, and cannot have both partners as co-commanders.
===Partner with itself===
The Mystery Booster 2 test card introduced "Partner with itself" (When this enters, target player may put Mothers Yamazaki into their hand from their library, then shuffle. A Commander deck can include two of this card, and they can be your commanders.) As long as you control exactly two permanents named Mothers Yamazaki, the “legend rule” doesn’t apply to them.
===Ready to Run===
Starting with Las Vegas 2024, the Unknown Event started producing cards based off the Magic players of LoadingReadyRun, which can only be "run" with each other. Eight cards were printed with this ability.
==Rules==
==Examples==
==Rulings==
;Partner with itself
*Mothers Yamazaki's "partner with itself" represents three abilities. The first is a triggered ability: "When this permanent enters, target player may search their library for a card named Mothers Yamazaki, reveal it, put it into their hand, then shuffle." 
*The second and third abilities represented by Mothers Yamazaki's "partner with itself" keyword modify the rules for deck construction in the Commander variant and have no function outside of that variant. They are "A Commander deck can have two cards named Mothers Yamazaki" and "You can designate two cards named Mothers Yamazaki as your commanders." 
*Both commanders start in the command zone, and the remaining 98 cards (or 58 cards in a Commander Draft game) of your deck are shuffled to become your library. 
*Once the game begins, your two commanders are tracked separately. If you cast one, you won't have to pay an additional {2} the first time you cast the other. A player loses the game after having been dealt 21 damage from one of them, not from both of them combined. Command Beacon's effect puts one into your hand from the command zone, not both. 
*An effect that checks whether you control your commander is satisfied if you control one or both of your two commanders. 
*The triggered ability of the "partner with itself" keyword still triggers in a Commander game. If your other commander has somehow ended up in your library, you can find it. You can also target another player, whether or not they have that card in their library.
==References==