"Defeat is no reason for retreat. It is a sign we must redouble our efforts to win this fight."

Valiant Knight

Other Knights you control get +1/+1.
{3}{W}{W}: Knights you control gain double strike until end of turn.

March of the Machine Commander

Core Set 2019

Core Set 2019 Promos

Because damage remains marked on a creature until it's removed as the turn ends, nonlethal damage dealt to a Knight you control may become lethal if Valiant Knight leaves the battlefield during that turn.

Multiple instances of double strike on the same creature are redundant.