Ward
From Archon Arcana
When a creature becomes warded, place a ward status counter on it. If a creature with a ward counter on it would be damaged, destroyed, or leave play, instead discard each ward counter on it. (Note: This prevents the creature from being tagged for destruction.)
While a creature has a ward counter on it, it cannot be warded again.
If a ward counter is placed on a creature after it has already been tagged for destruction, the ward counter will not prevent the creature from leaving play. However, it will prevent the creature from leaving play in other ways, such as being returned to hand.
—Official rules v1.7 December 2020
FFG Rulings
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Once a creature has been tagged for destruction, it's too late for the creature to be saved by a Ward. While a Ward can prevent a creature from being tagged for destruction, it will not prevent an already-tagged creature from leaving play.Source: Crucible Cast 17
What happens if a creature is Warded after being tagged for destruction, but before leaving play?
Once a creature has been tagged for destruction, it's too late for the creature to be saved by a Ward. While a Ward can prevent a creature from being tagged for destruction, it will not prevent an already-tagged creature from leaving play.
Source: Crucible Cast 17
Can I target a Warded or Enraged creature with the relevant effect and have it do nothing, similar to Stun?
Yes. Like Stun, both Ward and Enrage can target creatures that already have a token on them, the action will have no additional effect.
Source
Commentary
The Timing Chart clarifies that Ward's effect happens after effects that prevent damage are applied, but before Armor is used to prevent damage.