Each of the colours of mana is getting one of the gods of Theros.
The important thing about these cards is a little rule regarding your devotion. Your devotion is the number of a specific type of mana in the collective mana costs of all your current permanents. As long as this stays below five the gods don’t count as creatures!
This means that any spells designed to take out creatures will have no effect on them, rendering them pretty much invulnerable.
Of course, this leaves you restricted with what you can bring out onto the field, but given that they are Indestructible I doubt they’re in that much danger.
On top of this, they each come with some pretty nifty special abilities, one constantly in effect while the other you have to fork out a bit of mana for. Of course, being gods, they are also pretty heavy hitters. All for an impressively low mana cost to summon. No wonder they’re mythic rare!
Which of these gods will be worshipped in your deck?