Aurelia, the Law Above

Flying, vigilance, haste
Whenever a player attacks with three or more creatures, you draw a card.
Whenever a player attacks with five or more creatures, Aurelia deals 3 damage to each of your opponents and you gain 3 life.

Tajic, Blade of the Legion

Indestructible
Battalion — Whenever Tajic and at least two other creatures attack, Tajic gets +5/+5 until end of turn.

Zephyrim

Squad {2} (As an additional cost to cast this spell, you may pay {2} any number of times. When this creature enters, create that many tokens that are copies of it.)
Flying, vigilance
Miracle {1}{W} (You may cast this card for its miracle cost when you draw it if it's the first card you drew this turn.)

Firemane Avenger

Flying
Battalion — Whenever this creature and at least two other creatures attack, this creature deals 3 damage to any target and you gain 3 life.

Gary Clone

Squad {2} (As an additional cost to cast this spell, you may pay {2} any number of times. When this creature enters, create that many tokens that are copies of it.)
Whenever this creature attacks, each creature you control named Gary Clone gets +1/+0 until end of turn.

Silverwing Squadron

Flying, vigilance
Silverwing Squadron's power and toughness are each equal to the number of creatures you control.
Whenever this creature attacks, create a number of 2/2 white Knight creature tokens with vigilance equal to the number of opponents you have.

Wojek Halberdiers

Battalion — Whenever this creature and at least two other creatures attack, this creature gains first strike until end of turn.

Firefist Striker

Battalion — Whenever this creature and at least two other creatures attack, target creature can't block this turn.

Paladin Elizabeth Taggerdy

Battalion — Whenever Paladin Elizabeth Taggerdy and at least two other creatures attack, draw a card, then you may put a creature card with mana value X or less from your hand onto the battlefield tapped and attacking, where X is Paladin Elizabeth Taggerdy's power.

Ordruun Veteran

Battalion — Whenever this creature and at least two other creatures attack, this creature gains double strike until end of turn. (It deals both first-strike and regular combat damage.)

Fumiko the Lowblood

Fumiko has bushido X, where X is the number of attacking creatures. (Whenever this creature blocks or becomes blocked, it gets +X/+X until end of turn.)
Creatures your opponents control attack each combat if able.

Frontline Medic

Battalion — Whenever this creature and at least two other creatures attack, creatures you control gain indestructible until end of turn.
Sacrifice this creature: Counter target spell with {X} in its mana cost unless its controller pays {3}.

Boros Elite

Battalion — Whenever this creature and at least two other creatures attack, this creature gets +2/+2 until end of turn.

Sontaran General

Trample, haste
Battalion — Whenever this creature and at least two other creatures attack, for each opponent, goad up to one target creature that player controls. Those creatures can't block this turn. (Until your next turn, they attack each combat if able and attack a player other than you if able.)

Legion Loyalist

Haste
Battalion — Whenever this creature and at least two other creatures attack, creatures you control gain first strike and trample until end of turn and can't be blocked by creature tokens this turn.

Ultramarines Honour Guard

Squad {2} (As an additional cost to cast this spell, you may pay {2} any number of times. When this creature enters, create that many tokens that are copies of it.)
Other creatures you control get +1/+1.

Space Marine Devastator

Squad {2} (As an additional cost to cast this spell, you may pay {2} any number of times. When this creature enters, create that many tokens that are copies of it.)
Grav-cannon — When this creature enters, destroy up to one target artifact or enchantment.

Powder Ganger

Squad {2} (As an additional cost to cast this spell, you may pay {2} any number of times. When this creature enters, create that many tokens that are copies of it.)
When this creature enters, destroy up to one target artifact.

Boros Strike-Captain

Battalion — Whenever this creature and at least two other creatures attack, exile the top card of your library. During any turn you attacked with three or more creatures, you may play that card.