Leonin Vanguard

At the beginning of combat on your turn, if you control three or more creatures, this creature gets +1/+1 until end of turn and you gain 1 life.

Gird for Battle

Put a +1/+1 counter on each of up to two target creatures.

Boros Challenger

Mentor (Whenever this creature attacks, put a +1/+1 counter on target attacking creature with lesser power.)
{2}{R}{W}: This creature gets +1/+1 until end of turn.

Heroic Reinforcements

Create two 1/1 white Soldier creature tokens. Until end of turn, creatures you control get +1/+1 and gain haste. (They can attack and {T} this turn.)

Mountain

Ajani's Pridemate

Whenever you gain life, put a +1/+1 counter on this creature.

Skyknight Legionnaire

Haazda Marshal

Whenever this creature and at least two other creatures attack, create a 1/1 white Soldier creature token with lifelink.

Demotion

Enchant creature
Enchanted creature can't block, and its activated abilities can't be activated.

Healer's Hawk

Flying
Lifelink (Damage dealt by this creature also causes you to gain that much life.)

Boros Guildgate

This land enters tapped.
{T}: Add {R} or {W}.

Intervention

Intervention deals 3 damage to any target and you gain 3 life.

Integrity

Target creature gets +2/+2 until end of turn.

Integrity // Intervention

Boros Elite

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