Sol Ring

Sundown Pass

This land enters tapped unless you control two or more other lands.
{T}: Add {R} or {W}.

Clifftop Retreat

This land enters tapped unless you control a Mountain or a Plains.
{T}: Add {R} or {W}.

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.

Mountain

Command Tower

{T}: Add one mana of any color in your commander's color identity.

Boros Signet

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.

City of Brass

Whenever this land becomes tapped, it deals 1 damage to you.
{T}: Add one mana of any color.

Talisman of Conviction

{T}: Add {C}.
{T}: Add {R} or {W}. This artifact deals 1 damage to you.

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.

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.

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.

Selfless Samurai

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

Plains

Imperial Subduer

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

Spectator Seating

This land enters tapped unless you have two or more opponents.
{T}: Add {R} or {W}.