From the official rules: 616.1
Being able to kill anything for one or even zero mana is very powerful
I dove into the particulars of three-color cards in a Cube before we had the full preview
Evil Armor Class 22 (natural armor) Hit Points 364 (26d10 +182) Speed 50ft Saving Throws Strength +16, Constitution +14 Skills Athletics +16, Intimidation +10, Survival +13 Damage Resistances non-magical Bludgeoning, Piercing and Slashing Damage Immunities Fire, Lightning Condition Immunities Frightened, Blinded Senses 120ft Darkvision, 30ft Blindsight Languages Behemoth Challenge 21 The Behemoth can cast any of the following spell requiring no material components, Wisdom is his spellcasting modifier for these spells (Atk bonus +13, DC 21)
Im going to include a ton of cards that let you sacrifice creatures for profit, along with lots of creatures that are easy to sacrifice, to churn through the deck and slowly fill up the graveyard so that by the time you cast Izoni, youll get a big dose of sacrificial fodder, or perhaps a swarm to take down opponents life totals
It does read Mythic, even if it will likely be one of the cheaper Mythics