You can either build around a legendary creature and try to find cards that will complement this creatures abilities (referred as top-down building) or you can build around a mechanic/theme or combination of both that you find interesting and search for a Commander that will best fit to lead the deck (referred as bottom-up building)
they have Stage 1, Stage 2, and/or special mechanic evolutions
They allow you to go off again if everything failed the first time or kill the whole board in a single turn
Thankfully, a very large chunk of the initial Limited list managed to survive the cut
Avacyn, Angel of Hope (White Indestructible Creature) [c]Avacyn, Angel of Hope[/c], is incredible
A Universal Problem Currently, even at around $4, Bottle-Cap Blast doesnt seem like a bad pickup for many red-aligned artifact-focused decks