If a creature with devour and another creature are entering under your control at the same time, the creature with devour can't devour that other creature
It however is still considered to be in exile and not on the battlefield or your hand, meaning that there are much fewer ways for your opponent to be able to get rid of it before you can cast it
And if youve played games like Yu-Gi-Oh
Unfortunately, the way to do this in MTGA is really weird
Gift of Immortality is a excellent answer to any dies to Doom Blade arguments
While you can get stuck with a second land for the turn on top of your library, all too often when a Citadel hits the battlefield the table spends a good few minutes just watching the person who played it flip cards onto the battlefield, and then capping it all off by shuffling up to a combination of value, enter-the-battlefield effects, and a built-in Last-Ditch EffortLast-Ditch Effort