Here's my take on trying to make the Realm Eater fun & effective. From my experience RE isn't consistent if it's trying to start devouring on turn 3/4. This deck's gameplan is to start with some nice minions (mostly demons), start devouring when the enemy's occupied with removing your threats on turn 5+, then use the mobility capabilities (blinks and mounts) to stop his mid-to-endgame growth.

As for the atlas, the main idea was to have fun with the Mirage-synergic plays (especially Heirloom Lost -> Mirage to claim +2 mana diff.).