While that's not the most terrible idea, the likelihood in a Niv-Mizzet deck is that the other spell you're casting is a burn spell that could do the same, and I have to feel that you're going to be better off casting it by itself, rather than putting all your eggs in one basket
The impending ability appears only on a cycle of five mythic rare cards with Overlord in their name
Any or all of them are easily removed to add another supporting color
My top picks for artifacts include the Gateway and the Urzas Incubator for all your tribal build needs, and Crawlspace for your controlling and anti-Overrun/Craterhoof Behemoth tactics
If it stops being a creature, perhaps because your devotion to its color(s) decreased, it will be a legendary blue enchantment with no abilities
While WOE won't hold a candle to the most expensive cards from the LOTR set, it still has some high-value stuff