Crescendo of War

At the beginning of each upkeep, put a strife counter on Crescendo of War.
Attacking creatures get +1/+0 for each strife counter on Crescendo of War.
Blocking creatures you control get +1/+0 for each strife counter on Crescendo of War.

Crown of Doom

Whenever a creature attacks you or a planeswalker you control, it gets +2/+0 until end of turn.
{2}: Target player other than Crown of Doom's owner gains control of it. Activate only during your turn.

Mana-Charged Dragon

Flying, trample
Join forces — Whenever Mana-Charged Dragon attacks or blocks, each player starting with you may pay any amount of mana. Mana-Charged Dragon gets +X/+0 until end of turn, where X is the total amount of mana paid this way.

Death by Dragons

Each player other than target player creates a 5/5 red Dragon creature token with flying.

Domineering Will

Target player gains control of up to three target nonattacking creatures until end of turn. Untap those creatures. They block this turn if able.

Dulcet Sirens

{U}, {T}: Target creature attacks target opponent this turn if able.
Morph {U} (You may cast this card face down as a 2/2 creature for {3}. Turn it face up any time for its morph cost.)

Avatar of Slaughter

All creatures have double strike and attack each combat if able.

Edric, Spymaster of Trest

Whenever a creature deals combat damage to one of your opponents, its controller may draw a card.

Mystic Barrier

When Mystic Barrier enters and at the beginning of your upkeep, choose left or right.
Each player may attack only the nearest opponent in the last chosen direction and planeswalkers controlled by that opponent.

Aetherize

Return all attacking creatures to their owner's hand.

Archangel of Strife

Flying
As Archangel of Strife enters, each player chooses war or peace.
Creatures controlled by players who chose war get +3/+0.
Creatures controlled by players who chose peace get +0/+3.

Illusionist's Gambit

Cast this spell only during the declare blockers step on an opponent's turn.
Remove all attacking creatures from combat and untap them. After this phase, there is an additional combat phase. Each of those creatures attacks that combat if able. They can't attack you or planeswalkers you control that combat.