Vanilla means no rules text, so it can't have defender or any other ability. That in mind, here are the knobs they can play with:
Cost, Color, Supertype, Type, Subtype, Power, Toughness & Flavor
Depending on what the set it doing, there are a few different ways to make it 'feel' mythic. If it's a tribal set, making it above curve and in one or more relevant tribes might do it. If it's a set where types matter, making it an Enchantment Artifact Creature might do it (though that plays against the current philosophy of enchantment creatures feeling like enchantments).
From a flavor standpoint, they could do something like a planeswalker that lost its spark. Something like:
Gideon, Extinguished 2WW
Legendary Creature - Human Soldier
6/6
Someone on reddit suggested that they could also be introducing a new supertype.