Ward

Ward is an evergreen keyword ability introduced in Strixhaven: School of Mages. Ward is a triggered ability.

Description
Whenever a permanent with ward becomes the target of a spell or ability an opponent controls, counter it unless that player pays an additional cost.

Before it was keyworded, Ward was known as Frost armor. Early examples with this mechanic were Frost Titan and Diffusion Sliver. A variant on cards like Boreal Elemental and Callaphe, Beloved of the Sea simply increased the cost of targeting, with no triggered ability built in.

The two most common forms are costing additional mana (in white, blue, and green) and costing additional life (in black and red). These two approaches both protect against removal but ask different things of the rest of your deck and give opponents different incentives for when to bite the bullet and remove the warded creature. Going forward, R&D announced some more unique ward costs as well.

Any spell or ability controlled by an opponent can be affected by ward. This includes Aura spells, triggered abilities, and anything else that target a permanent with ward. Spells and abilities that don't target won't cause ward to trigger.

Ruling

 * If a player casts a spell that targets multiple permanents their opponent controls with ward, each of those ward abilities will trigger. If that player doesn't pay for all of them, the spell will be countered.
 * A spell or ability that can't be countered that targets one or more permanents with Ward, ignore the Ward ability completely. The Ward triggers, but produces no effect on resolution,