No Dragons will fight Imrik. If they are in base contact with other models (and not in a challenge) then they fight them instead, otherwise they may do nothing. Their riders (if they have any) still fight as normal.
Models with this special rule have Dodge (6+) special rule in close combat. However, this cannot be used against enemies that attack before the model with Elven Grace.
Models with this rule (but not any mounts) may re-roll all To Hit rolls of 1 when making close combat attacks.
If your opponent's army roster contains one or more models from Warhammer: Dark Elves, models with this special rule re-roll all failed Panic tests and have Immunity (Fear).
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Infantry (Special Character)