Brisela, Voice of Nightmares
Legendary Creature — Eldrazi Angel
Flying, first strike, vigilance, lifelink
Your opponents can't cast spells with converted mana cost 3 or less.
Upon discovering what had become of her sisters, Sigarda could only weep.
Illustrated by
From the Vault: Transform#5bMythicEnglishLegality
Rulings
In a Commander game, your commander may be Bruna, the Fading Light or Gisela, the Broken Blade, and the other may be in your deck. If they meld into Brisela, Voice of Nightmares, Brisela will also be your commander; but if Brisela leaves the battlefield, only the card chosen as your commander at the start of the game may be put into the command zone.
A “when you cast” triggered ability resolves before the original spell resolves. It resolves even if the original spell is countered, and the original spell resolves even if the triggered ability is countered.
Effects that increase or reduce the cost to cast a spell (such as those of escalate and emerge) don’t affect the spell’s converted mana cost, so they won’t change whether Brisela’s last ability restricts that spell from being cast.
For spells with 
in their mana costs, use the value chosen for X to determine if the spell’s converted mana cost is 3 or less. For example, your opponent could cast Burn from Within (a spell with mana cost 
) with X equal to 3, but not with X equal to 2.
For more information on meld cards, see the Eldritch Moon mechanics article (https://magic.wizards.com/en/articles/archive/feature/eldritch-moon-mechanics-2016-06-27).