If an attacking creature loses haste, perhaps because Fervor leaves the battlefield after attackers have been declared, it won't be removed from combat.

Fervor : règles, fonctionnement et interactions (MTG)

Fervor is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

Creatures you control have haste. (They can attack and as soon as they come under your control.)

Complete guide

Fervor is a classic red enchantment that changes the tempo of the game by granting all your creatures haste. It allows you to ignore the usual rules of summoning sickness, turning every creature card in your hand into an immediate threat.

What It Does

Fervor provides a static ability that gives every creature you control haste. This means any creature you currently have on the battlefield, or any that enter the battlefield later while Fervor is active, can attack or use abilities with the tap symbol the same turn they come under your control.

How It Resolves

Once Fervor is on the battlefield, its effect is continuous. As soon as a creature enters the battlefield under your control, the game checks for haste. Because Fervor is an enchantment, it doesn't target specific creatures; it simply applies to all of them as long as the enchantment remains in play.

Common Mistakes

A common misconception is that losing Fervor during combat stops your creatures from attacking. According to official rulings, if Fervor leaves the battlefield after you have already declared attackers, those creatures are not removed from combat. They have already been legally declared as attackers, and losing haste at that point does not undo the action.

When to Play It

Fervor is best utilized in aggressive decks that rely on creature-based strategies. By eliminating the one-turn delay normally required for creatures to act, you can maintain pressure on your opponent and capitalize on board states before they have time to set up their own defenses.

Interaction examples

Immediate Pressure

With Fervor on the battlefield, you cast a creature. Instead of waiting for your next turn to attack, the creature gains haste immediately, allowing you to declare it as an attacker during your current combat phase.

Enchantment Synergy

Impact Tremors

When you play a creature, Impact Tremors triggers to deal 1 damage to each opponent. Simultaneously, Fervor ensures that same creature can attack immediately, combining passive burn damage with direct combat damage in a single turn.

Escaping the Grave

Underworld Breach

If you use Underworld Breach to cast a creature from your graveyard, that creature would normally be vulnerable for a turn. However, with Fervor in play, that creature can attack the same turn it is escaped from the graveyard, maximizing the value of your temporary window to cast spells.

Guide written with AI from the official text and rulings. Official English text prevails.

How it works : Fervor

Original English text — Wizards of the Coast / Scryfall

#1July 1, 2012· Wizards of the Coast
If an attacking creature loses haste, perhaps because Fervor leaves the battlefield after attackers have been declared, it won't be removed from combat.
No other card is named in this ruling.