Proud Mentor
Creature — Human Warrior
Partner with Impetuous Protege (When this creature enters, target player may put Impetuous Protege into their hand from their library, then shuffle.)
, 
: Tap target creature.
"Get ready, son."
Jakub Kasper
Battlebond Promos (PBBD)
• #20sRulings
A nonlegendary creature can't be your commander, even if it has a "partner with" ability.
(wotc • 2018-06-08)
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.
(wotc • 2018-06-08)
"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."
(wotc • 2018-06-08)
Rulings
A nonlegendary creature can't be your commander, even if it has a "partner with" ability.
(wotc • 2018-06-08)
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.
(wotc • 2018-06-08)
"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."
(wotc • 2018-06-08)