Does Anivia's damage effect trigger when she is moved to a battlefield by an effect (rather than being moved there normally to start a showdown)?

Ruling: Anivia's effect triggers when she becomes an attacker at a battlefield, regardless of how she arrives there. If she is moved to a battlefield where she becomes the attacker (such as being moved to an opponent-controlled battlefield), her effect activates.

Nuances:

• If Anivia is already at a battlefield and another unit moves to her (like with Stormbringer), she is not the attacker and her effect does not trigger
• The key factor is whether Anivia receives the "attacker" designation, not the method by which she arrives at the battlefield