Peerless Samurai

Menace (This creature can't be blocked except by two or more creatures.)
Whenever a Samurai or Warrior you control attacks alone, the next spell you cast this turn costs {1} less to cast.

Ancestral Katana

Whenever a Samurai or Warrior you control attacks alone, you may pay {1}. When you do, attach Ancestral Katana to it.
Equipped creature gets +2/+1.
Equip {3} ({3}: Attach to target creature you control. Equip only as a sorcery.)

Mountain

Beskir Shieldmate

When Beskir Shieldmate dies, create a 1/1 white Human Warrior creature token.

Herald of Dromoka

Vigilance
Other Warrior creatures you control have vigilance.

Eiganjo Exemplar

Whenever a Samurai or Warrior you control attacks alone, it gets +1/+1 until end of turn.

Rush of Battle

Creatures you control get +2/+1 until end of turn. Warrior creatures you control gain lifelink until end of turn. (Damage dealt by those Warriors also causes their controller to gain that much life.)

Javelin of Lightning

Flash
When Javelin of Lightning enters, attach it to target creature you control.
During your turn, equipped creature gets +2/+0 and has first strike.
Equip {4} ({4}: Attach to target creature you control. Equip only as a sorcery.)

Plains

Imperial Subduer

Whenever a Samurai or Warrior you control attacks alone, tap target creature you don't control.

Cartouche of Solidarity

Enchant creature you control
When Cartouche of Solidarity enters, create a 1/1 white Warrior creature token with vigilance.
Enchanted creature gets +1/+1 and has first strike. (It deals combat damage before creatures without first strike.)

Resolute Strike

Target creature gets +2/+2 until end of turn. If it's a Warrior, you may attach an Equipment you control to it.