Selfless Samurai

Whenever a Samurai or Warrior you control attacks alone, it gains lifelink until end of turn.
Sacrifice Selfless Samurai: Another target creature you control gains indestructible until end of turn. (Damage and effects that say "destroy" don't destroy it.)

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.)

Archetype of Aggression

Creatures you control have trample.
Creatures your opponents control lose trample and can't have or gain trample.

Plains

Mountain

Banishing Slash

Destroy up to one target artifact, enchantment, or tapped creature. Then if you control an artifact and an enchantment, create a 2/2 white Samurai creature token with vigilance.

Wind-Scarred Crag

This land enters tapped.
When this land enters, you gain 1 life.
{T}: Add {R} or {W}.

Kindled Fury

Target creature gets +1/+0 and gains first strike until end of turn. (It deals combat damage before creatures without first strike.)

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.

Imperial Subduer

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