Ancient Animus

Put a +1/+1 counter on target creature you control if it's legendary. Then it fights target creature an opponent controls. (Each deals damage equal to its power to the other.)

Dangerous

All creatures able to block target creature this turn do so.
Fuse (You may cast one or both halves of this card from your hand.)

Armed

Target creature gets +1/+1 and gains double strike until end of turn.
Fuse (You may cast one or both halves of this card from your hand.)

Armed // Dangerous

Rivals' Duel

Choose two target creatures that share no creature types. Those creatures fight each other. (Each deals damage equal to its power to the other.)

Gorm the Great

Partner with Virtus the Veiled (When this creature enters, target player may put Virtus into their hand from their library, then shuffle.)
Vigilance
Gorm must be blocked if able, and Gorm must be blocked by two or more creatures if able.

Arena

{3}, {T}: Tap target creature you control and target creature of an opponent's choice they control. Those creatures fight each other. (Each deals damage equal to its power to the other.)

Domri, Anarch of Bolas

Creatures you control get +1/+0.
+1: Add {R} or {G}. Creature spells you cast this turn can't be countered.
−2: Target creature you control fights target creature you don't control.

Go for Blood

Target creature you control fights target creature you don't control. (Each deals damage equal to its power to the other.)
Cycling {1} ({1}, Discard this card: Draw a card.)

Aggressive Mammoth

Trample (This creature can deal excess combat damage to the player or planeswalker it's attacking.)
Other creatures you control have trample.

Blizzard Brawl

Choose target creature you control and target creature you don't control. If you control three or more snow permanents, the creature you control gets +1/+0 and gains indestructible until end of turn. Then those creatures fight each other. (Each deals damage equal to its power to the other.)

Duel for Dominance

Coven — Choose target creature you control and target creature you don't control. If you control three or more creatures with different powers, put a +1/+1 counter on the chosen creature you control. Then the chosen creatures fight each other. (Each deals damage equal to its power to the other.)

Breaker of Armies

All creatures able to block this creature do so.

Clash of Titans

Target creature fights another target creature. (Each deals damage equal to its power to the other.)

Apex Altisaur

When this creature enters, it fights up to one target creature you don't control.
Enrage — Whenever this creature is dealt damage, it fights up to one target creature you don't control.

Arni Slays the Troll

(As this Saga enters and after your draw step, add a lore counter. Sacrifice after III.)
I — Target creature you control fights up to one target creature you don't control.
II — Add {R}. Put two +1/+1 counters on up to one target creature you control.
III — You gain life equal to the greatest power among creatures you control.

Prey Upon

Target creature you control fights target creature you don't control. (Each deals damage equal to its power to the other.)

Domri Rade

+1: Look at the top card of your library. If it's a creature card, you may reveal it and put it into your hand.
−2: Target creature you control fights another target creature.
−7: You get an emblem with "Creatures you control have double strike, trample, hexproof, and haste."

Magus of the Arena

Epic Confrontation

Target creature you control gets +1/+2 until end of turn. It fights target creature you don't control. (Each deals damage equal to its power to the other.)

Nacatl War-Pride

This creature must be blocked by exactly one creature if able.
Whenever this creature attacks, create X tokens that are copies of it and that are tapped and attacking, where X is the number of creatures defending player controls. Exile the tokens at the beginning of the next end step.

Nemesis Mask

All creatures able to block equipped creature do so.
Equip {3} ({3}: Attach to target creature you control. Equip only as a sorcery.)

Brash Taunter

Indestructible
Whenever this creature is dealt damage, it deals that much damage to target opponent.
{2}{R}, {T}: This creature fights another target creature.

Joraga Invocation

Each creature you control gets +3/+3 until end of turn and must be blocked this turn if able.

Gruul Ragebeast

Whenever this creature or another creature you control enters, that creature fights target creature an opponent controls.

Contested Cliffs

{T}: Add {C}.
{R}{G}, {T}: Target Beast creature you control fights target creature an opponent controls. (Each deals damage equal to its power to the other.)

Ulvenwald Tracker

{1}{G}, {T}: Target creature you control fights another target creature.

Ezuri's Predation

For each creature your opponents control, create a 4/4 green Phyrexian Beast creature token. Each of those tokens fights a different one of those creatures.

Foe-Razer Regent

Flying
When this creature enters, you may have it fight target creature you don't control.
Whenever a creature you control fights, put two +1/+1 counters on it at the beginning of the next end step.

Inescapable Brute

Wither (This deals damage to creatures in the form of -1/-1 counters.)
This creature must be blocked if able.

Satyr Piper

{3}{G}: Target creature must be blocked this turn if able.

Neyith of the Dire Hunt

Whenever one or more creatures you control fight or become blocked, draw a card.
At the beginning of combat on your turn, you may pay {2}{R/G}. If you do, double target creature's power until end of turn. That creature must be blocked this combat if able. ({R/G} can be paid with either {R} or {G}.)

Pit Fight

Target creature you control fights another target creature. (Each deals damage equal to its power to the other.)