Isshin, Two Heavens as One

If a creature attacking causes a triggered ability of a permanent you control to trigger, that ability triggers an additional time.

Akki Ronin

Whenever a Samurai or Warrior you control attacks alone, you may discard a card. If you do, draw a card.

Kentaro, the Smiling Cat

Bushido 1 (Whenever this creature blocks or becomes blocked, it gets +1/+1 until end of turn.)
You may pay {X} rather than pay the mana cost for Samurai spells you cast, where X is that spell's mana value.

Iizuka the Ruthless

Bushido 2 (Whenever this creature blocks or becomes blocked, it gets +2/+2 until end of turn.)
{2}{R}, Sacrifice a Samurai: Samurai creatures you control gain double strike until end of turn.

Asari Captain

Haste
Whenever a Samurai or Warrior you control attacks alone, it gets +1/+0 until end of turn for each Samurai or Warrior you control.

Raiyuu, Storm's Edge

First strike
Whenever a Samurai or Warrior you control attacks alone, untap it. If it's the first combat phase of the turn, there is an additional combat phase after this phase.

Ironsoul Enforcer

Whenever this creature or a commander you control attacks alone, return target artifact card from your graveyard to the battlefield.

Konda's Hatamoto

Bushido 1 (Whenever this creature blocks or becomes blocked, it gets +1/+1 until end of turn.)
As long as you control a legendary Samurai, this creature gets +1/+2 and has vigilance. (Attacking doesn't cause this creature to tap.)

Kitsune Blademaster

First strike
Bushido 1 (Whenever this creature blocks or becomes blocked, it gets +1/+1 until end of turn.)

Konda, Lord of Eiganjo

Vigilance, indestructible
Bushido 5 (Whenever this creature blocks or becomes blocked, it gets +5/+5 until end of turn.)

Eiganjo Exemplar

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

Norika Yamazaki, the Poet

Vigilance
Whenever a Samurai or Warrior you control attacks alone, you may cast target enchantment card from your graveyard this turn.

Indebted Samurai

Bushido 1 (Whenever this creature blocks or becomes blocked, it gets +1/+1 until end of turn.)
Whenever a Samurai you control dies, you may put a +1/+1 counter on this creature.

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.

Akki Battle Squad

Whenever one or more modified creatures you control attack, untap all modified creatures you control. After this phase, there is an additional combat phase. This ability triggers only once each turn. (Equipment, Auras you control, and counters are modifications.)

Heiko Yamazaki, the General

Trample
Whenever a Samurai or Warrior you control attacks alone, you may cast target artifact card from your graveyard this turn.

Imperial Subduer

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