Haunted One

This Background sits on the battlefield and hands every one of your commander creatures a tap-triggered team pump: when your leader becomes tapped, it and everything sharing a creature type with it each get +2/+0 and undying for the turn. Attacking is the obvious on-ramp, but the trigger fires on any tap you can manufacture, from convoke to crewing to activated abilities that spend a tap in their cost. The undying half is doing the quieter work: for one turn your on-type board attacks into blocks or shrugs off targeted removal, because anything without a +1/+1 counter comes back a size larger. That folds graveyard recursion into the same window as the alpha strike, so the punishment for blocking and the punishment for killing arrive together. The type-matching restriction is what pins it to a tribe rather than a global anthem: the pump chains only across creatures sharing a type with the commander, so the deckbuilding cost is committing to a creature type deep enough that "shares a type with your commander" describes most of your board. Point it at a leader whose type is well-supported and a wide board becomes a one-turn threat that is hard to trade with; point it at an off-tribe general and it barely registers. The demand runs inward before it runs at the opponent: the deck has to be coherent first, and only then does the payoff pay.