It just fails you too often and you die horribly as a result
(Although be warned: the median value is only $1.25, so this average value is driven up by a small number of expensive rares, and many individual packs of Double Masters will hold two bulk-level rares.) With 42 rares in the typical box, this adds another $133 to the expected value of a box, which means the rares and mythics alone currently add a total of $267 to the value of a Double Masters booster box
As far as changes to make to the budget build of the deck, I wouldn't change a single card
If it's your turn, you control Coram, and another player has permission to play a card in a graveyard that was put there from a library this turn (perhaps because it's an instant card they own that has flashback), whoever gets priority sooner will have the first chance to play that card
The Cube Prize Pack bonus sheet contains: Mythics: Dack Fayden, Leovold, Emissary of Trest, Titania, Protector of Argoth, Torsten, Founder of Benalia, Tourach, Dread Cantor Rares: Glimmer Lens, Death-Greeters Champion, Myr Battlesphere, Winds of Abandon, Woodfall Primus, Dress Down, Carnage Interpreter, Unmarked Grave, Upheaval, Echo of Eons, Survival of the Fittest, Coveted Jewel, Parallax Wave Uncommons: Zuran Orb, Pentad Prism, Vampire Hexmage, Pyrokinesis, Fire Covenant Commons: Mine Collapse, Snuff Out, Seething Song MTG Arena 'WIN' Rewards When you win a game in MTG Arenaany gameyoull receive certain rewards