Build-around Elemental Uprising and Grinning Ignus/Smokebraider providing Ferocious (and eventually Formidable) turns earlier: Barrage of Boulders 2Red (3) Sorcery Barrage of Boulders deals 1 damage to each creature you don't control.  Ferocious — If you control a creature with power 4 or greater, creatures can't block this turn.  Khans of Tarkir (Common)
Crater's Claws Crater's Claws Variable ColorlessRed (1) Sorcery Crater's Claws deals X damage to any target.  Ferocious — Crater's Claws deals X plus 2 damage instead.  Khans of Tarkir (Rare)
Dragon Grip Dragon Grip 2Red (3) Enchantment — Aura Ferocious — you may cast Dragon Grip as though it had flash. (You may cast it any time you could cast an instant.)  Enchant creature  Enchanted creature gets +2/+0 and has first strike.  Khans of Tarkir (Uncommon)
Feed the Clan Feed the Clan 1Green (2) Instant You gain 5 life.  Ferocious — You gain 10 life instead.  Khans of Tarkir (Common)
Flamewake Phoenix Flamewake Phoenix 1RedRed (3) Creature — Phoenix (2/2) Flying, haste  Flamewake Phoenix attacks each combat if able.  Ferocious — At the beginning of combat on your turn, you may pay Red. If you do, return Flamewake Phoenix from your graveyard to the battlefield.  Fate Reforged (Rare)
Force Away Force Away 1Blue (2) Instant Return target creature to its owner's hand.  Ferocious — you may draw a card. If you do, discard a card.  Khans of Tarkir (Common)
Frontier Mastodon Frontier Mastodon 2Green (3) Creature — Elephant (3/2) Ferocious — Frontier Mastodon enters the battlefield with a +1/+1 counter on it.  Fate Reforged (Common)
Heir of the Wilds Heir of the Wilds 1Green (2) Creature — Human Warrior (2/2) Deathtouch  Ferocious — Whenever Heir of the Wilds attacks, Heir of the Wilds gets +1/+1 until end of turn.  Khans of Tarkir (Uncommon)
Icy Blast Icy Blast Variable ColorlessBlue (1) Instant Tap X target creatures.  Ferocious — those creatures don't untap during their controllers' next untap steps.  Khans of Tarkir (Rare)
Roar of Challenge Roar of Challenge 2Green (3) Sorcery All creatures able to block target creature this turn do so.  Ferocious — That creature gains indestructible until end of turn.  Khans of Tarkir (Uncommon)
Savage Punch Savage Punch 1Green (2) Sorcery Target creature you control fights target creature you don't control.  Ferocious — The creature you control gets +2/+2 until end of turn before it fights.  Khans of Tarkir (Common)
See the Unwritten See the Unwritten 4GreenGreen (6) Sorcery Reveal the top eight cards of your library. You may put a creature card from among them onto the battlefield. Put the rest into your graveyard.  Ferocious — you may put two creature cards onto the battlefield instead of one.  Khans of Tarkir (Mythic Rare)
Shaman of the Great Hunt Shaman of the Great Hunt 3Red (4) Creature — Orc Shaman (4/2) Haste  Whenever a creature you control deals combat damage to a player, put a +1/+1 counter on it.  Ferocious — 2Green or BlueGreen or Blue: Draw a card for each creature you control with power 4 or greater.  Fate Reforged (Mythic Rare)
Shamanic Revelation Shamanic Revelation 3GreenGreen (5) Sorcery Draw a card for each creature you control.  Ferocious — You gain 4 life for each creature you control with power 4 or greater.  Commander 2019 (Rare)
Other Versions Fate Reforged (Rare)Commander 2016 (Rare)
Stubborn Denial Stubborn Denial Blue (1) Instant Counter target noncreature spell unless its controller pays 1.  Ferocious — counter that spell instead.  Khans of Tarkir (Uncommon)
Temur Battle Rage Temur Battle Rage 1Red (2) Instant Target creature gains double strike until end of turn. (It deals both first-strike and regular combat damage.)  Ferocious — That creature also gains trample until end of turn.  Fate Reforged (Common)
Whisperer of the Wilds Whisperer of the Wilds 1Green (2) Creature — Human Shaman (0/2) Tap: Add Green.  Ferocious — Tap: Add GreenGreen. Activate this ability only.  Fate Reforged (Common)
Wild Slash Wild Slash Red (1) Instant Ferocious — damage can't be prevented this turn.  Wild Slash deals 2 damage to any target.  Fate Reforged (Uncommon)
Winds of Qal Sisma Winds of Qal Sisma 1Green (2) Instant Prevent all combat damage that would be dealt this turn.  Ferocious — instead prevent all combat damage that would be dealt this turn by creatures your opponents control.