This is cheating, and this sort of behavior can get you kicked out of a draft, disqualified from an event, or even banned from the DCI
On later turns, instead you cast it as intended for a hand refill
Mithril Coat Taking Darksteel Plate, giving it flash, and letting it attach itself to a legendary creature when it enters the battlefield makes Mithril Coat an incredibly potent card for any deck where your commander is a creature that ends up dying a lot
I always recommend buying from a local game store over buying online because you can see the cards in person, but you wont always be able to find the cards you are in search of
Most of these EDH precons have a few subthemes stapled together in their builds, and you can usually shift the legendary creatures around to make the deck fit if you make a few changes to it out of your existing collection
It has a "fossil counter" mechanic that interacts with other cards