Inner-Flame Igniter

{2}{R}: Creatures you control get +1/+0 until end of turn. If this is the third time this ability has resolved this turn, creatures you control gain first strike until end of turn.

Fearless Liberator

Boast — {2}{R}: Create a 2/1 red Dwarf Berserker creature token. (Activate only if this creature attacked this turn and only once each turn.)

Frenzied Raider

Whenever you activate a boast ability, put a +1/+1 counter on Frenzied Raider.

Tuskeri Firewalker

Boast — {1}: Exile the top card of your library. You may play that card this turn. (Activate only if this creature attacked this turn and only once each turn.)

Mountain

Pursue Glory

Attacking creatures get +2/+0 until end of turn.
Cycling {2} ({2}, Discard this card: Draw a card.)

Hagi Mob

Boast — {1}{R}: Hagi Mob deals 1 damage to any target. (Activate only if this creature attacked this turn and only once each turn.)

Harnfel, Horn of Bounty

Discard a card: Exile the top two cards of your library. You may play those cards this turn.

Birgi, God of Storytelling

Whenever you cast a spell, add {R}. Until end of turn, you don't lose this mana as steps and phases end.
Creatures you control can boast twice during each of your turns rather than once.

Birgi, God of Storytelling // Harnfel, Horn of Bounty

Goblin Oriflamme

Attacking creatures you control get +1/+0.

Dogpile

Dogpile deals damage to any target equal to the number of attacking creatures you control.

Fearless Pup

First strike
Boast — {2}{R}: Fearless Pup gets +2/+0 until end of turn. (Activate only if this creature attacked this turn and only once each turn.)

Thriving Bluff

Thriving Bluff enters tapped. As it enters, choose a color other than red.
{T}: Add {R} or one mana of the chosen color.

Dragonkin Berserker

First strike
Boast abilities you activate cost {1} less to activate for each Dragon you control.
Boast — {4}{R}: Create a 5/5 red Dragon creature token with flying. (Activate only if this creature attacked this turn and only once each turn.)