Angelic Exaltation

Whenever a creature you control attacks alone, it gets +X/+X until end of turn, where X is the number of creatures you control.

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.

Risona, Asari Commander

Haste
Whenever Risona, Asari Commander deals combat damage to a player, if it doesn't have an indestructible counter on it, put an indestructible counter on it.
Whenever combat damage is dealt to you, remove an indestructible counter from Risona.

Combat Celebrant

If Combat Celebrant hasn't been exerted this turn, you may exert it as it attacks. When you do, untap all other creatures you control and after this phase, there is an additional combat phase. (An exerted creature won't untap during your next untap step.)

Akiri, Fearless Voyager

Whenever you attack a player with one or more equipped creatures, draw a card.
{W}: You may unattach an Equipment from a creature you control. If you do, tap that creature and it gains indestructible until end of turn.

Commander's Sphere

{T}: Add one mana of any color in your commander's color identity.
Sacrifice Commander's Sphere: Draw a card.

Tempered in Solitude

Whenever a creature you control attacks alone, exile the top card of your library. You may play that card this turn.

Arcane Signet

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

Ironsoul Enforcer

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

O-Naginata

O-Naginata can be attached only to a creature with power 3 or greater.
Equipped creature gets +3/+0 and has trample.
Equip {2} ({2}: Attach to target creature you control. Equip only as a sorcery.)

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.)

No-Dachi

Equipped creature gets +2/+0 and has first strike.
Equip {3} ({3}: Attach to target creature you control. Equip only as a sorcery.)

City on Fire

Convoke (Your creatures can help cast this spell. Each creature you tap while casting this spell pays for {1} or one mana of that creature's color.)
If a source you control would deal damage to a permanent or player, it deals triple that damage instead.

Reinforced Ronin

Haste
At the beginning of your end step, return Reinforced Ronin to its owner's hand.
Channel — {1}{R}, Discard Reinforced Ronin: Draw a card.

Fighter Class

(Gain the next level as a sorcery to add its ability.)
When Fighter Class enters, search your library for an Equipment card, reveal it, put it into your hand, then shuffle.
{1}{R}{W}: Level 2
Equip abilities you activate cost {2} less to activate.
{3}{R}{W}: Level 3
Whenever a creature you control attacks, up to one target creature blocks it this combat if able.

Open the Armory

Search your library for an Aura or Equipment card, reveal it, put it into your hand, then shuffle.

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.

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.

Path to Exile

Exile target creature. Its controller may search their library for a basic land card, put that card onto the battlefield tapped, then shuffle.

Plains

Goro-Goro, Disciple of Ryusei

{R}: Creatures you control gain haste until end of turn.
{3}{R}{R}: Create a 5/5 red Dragon Spirit creature token with flying. Activate only if you control an attacking modified creature. (Equipment, Auras you control, and counters are modifications.)

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.

Sunblade Samurai

Vigilance
Channel — {2}, Discard Sunblade Samurai: Search your library for a basic Plains card, reveal it, put it into your hand, then shuffle. You gain 2 life.

Boros Signet

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.)

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.)

Mountain

Sol Ring

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.

Farewell

Choose one or more —
• Exile all artifacts.
• Exile all creatures.
• Exile all enchantments.
• Exile all graveyards.