This is a Knight that only costs two colorless and one White Mana, so with four in your deck, the odds are in your favor for getting and keeping at least one out in play, if not two, in longer drawn out games
This frees up space in your decks to run a wider variety of spells, since you can count on tutoring up whatever the situation calls for
Theres a different shuffle feel between Eclipse and Dragon Shields, and I prefer the Eclipse ones in that regard
Just casting this dragon avatar gives you strong card advantage, and it can be tutored and cast via Bring to Light, giving birth to the Niv-to-Light deck
The trigger event doesn't have to specifically refer to legendary permanents or to artifacts, nor does it have to specifically refer to when something "leaves the battlefield." For example, an ability that triggers "whenever a creature dies" would trigger twice if a legendary creature or an artifact creature dies while Gandalf the White is on the battlefield, as would an ability that triggers "whenever a permanent is put into a graveyard from the battlefield." Look at each legendary permanent and each artifact as it exists on the battlefield, taking into account continuous effects, to determine whether any triggered abilities will trigger multiple times