Cazur, Ruthless Stalker — ruling 1

"Partner with [name]" represents two abilities. The first is a triggered ability: "When this permanent enters the battlefield, target player may search their library for a card named [name], reveal it, put it into their hand, then shuffle their library."

Cazur, Ruthless Stalker — ruling 2

Note that the target player searches their library (which may be affected by effects such as that of Stranglehold) and that the card they find is revealed, even though these words aren't included in the ability's reminder text.

Cazur, Ruthless Stalker — ruling 3

The second ability represented by the "partner with [name]" keyword modifies the rules for deck construction in the Commander variant and has no function outside of that variant. If a legendary creature card with "partner with [name]" is designated as your commander, the named legendary creature card can also be designated as your commander.

Cazur, Ruthless Stalker — ruling 4

If your Commander deck has two commanders, you can only include cards whose own color identities are also found in your commanders' combined color identities. If Haldan and Pako are your commanders, your deck may contain cards with blue, red, and/or green in their color identity, but not cards with white or black.

Cazur, Ruthless Stalker — ruling 5

Both commanders start in the command zone, and the remaining 98 cards of your deck are shuffled to become your library.

Cazur, Ruthless Stalker — ruling 6

A creature with a "partner with" ability can't partner with any creature other than its designated partner. Losing a partner ability during the game doesn't cause either to cease to be your commander.

Cazur, Ruthless Stalker — ruling 7

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.

Cazur, Ruthless Stalker — ruling 8

The triggered ability of the "partner with" 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 who might have that card in their library.

Cazur, Ruthless Stalker : règles, fonctionnement et interactions (MTG)

Cazur, Ruthless Stalker is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

Partner with Ukkima, Stalking Shadow (When this creature enters, target player may put Ukkima into their hand from their library, then shuffle.) Whenever a creature you control deals combat damage to a player, put a +1/+1 counter on that creature.

How it works : Cazur, Ruthless Stalker

Original English text — Wizards of the Coast / Scryfall

#1April 17, 2020· Wizards of the Coast
"Partner with [name]" represents two abilities. The first is a triggered ability: "When this permanent enters the battlefield, target player may search their library for a card named [name], reveal it, put it into their hand, then shuffle their library."
No other card is named in this ruling.
#2April 17, 2020· Wizards of the Coast
Note that the target player searches their library (which may be affected by effects such as that of Stranglehold) and that the card they find is revealed, even though these words aren't included in the ability's reminder text.
No other card is named in this ruling.
#3April 17, 2020· Wizards of the Coast
The second ability represented by the "partner with [name]" keyword modifies the rules for deck construction in the Commander variant and has no function outside of that variant. If a legendary creature card with "partner with [name]" is designated as your commander, the named legendary creature card can also be designated as your commander.
No other card is named in this ruling.
#4April 17, 2020· Wizards of the Coast
If your Commander deck has two commanders, you can only include cards whose own color identities are also found in your commanders' combined color identities. If Haldan and Pako are your commanders, your deck may contain cards with blue, red, and/or green in their color identity, but not cards with white or black.
No other card is named in this ruling.
#5April 17, 2020· Wizards of the Coast
Both commanders start in the command zone, and the remaining 98 cards of your deck are shuffled to become your library.
No other card is named in this ruling.
#6April 17, 2020· Wizards of the Coast
A creature with a "partner with" ability can't partner with any creature other than its designated partner. Losing a partner ability during the game doesn't cause either to cease to be your commander.
No other card is named in this ruling.
#7April 17, 2020· Wizards of the Coast
Once the game begins, your two commanders are tracked separately. If you cast one, you won't have to pay an additional 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.
No other card is named in this ruling.
#8April 17, 2020· Wizards of the Coast
The triggered ability of the "partner with" 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 who might have that card in their library.
No other card is named in this ruling.

Interactions with other cards

These cards' text mentions Cazur, Ruthless Stalker.

Ukkima, Stalking Shadow

Partner with Cazur, Ruthless Stalker (When this creature enters, target player may put Cazur into their hand from their library, then shuffle.) Ukkima can't be blocked. When Ukkima leaves the battlefield, it deals X damage to target player and you gain X life, where X is its power.