Partner has been a mechanic in Magic the Gathering since the Commander 2016 set and has been controversial since its introduction. Partner allows for a Commander deck to have two commanders so long as they both have the keyword 'Partner'. Generally, people disliked Partner as the commanders with this skill provided free card advantage and access to a wide range of colors without the drawback of having a color-intensive cost. Later, a variant of the mechanic called 'Partner With' meant that these commanders could only be paired with specific partners. They also tried to release Partner cards that were mono-colored, limiting the number of colors that two partner cards could cover. More recently another version of the mechanic has come out with the new Doctor Who Universes Beyond set with the 'Doctor's Companion' mechanic, which allows cards with the mechanic to be paired with any Time Lord card in the command zone.
Source：https://www.cbr.com/magic-the-gathering-partner-commanders-needed/
