Xenagos, God of Revels

• WOTC Official Reminder Textofficial rules
  Indestructible — Effects that say "destroy" don't destroy this permanent. A creature with indestructible can't be destroyed by damage.

• WWizards of the Coast2013-09-15
  Official Ruling
  Hybrid mana symbols, monocolored hybrid mana symbols, and Phyrexian mana symbols do count toward your devotion to their color(s).
• WWizards of the Coast2013-09-15
  Official Ruling
  Numeric mana symbols (, , and so on) in mana costs of permanents you control don't count toward your devotion to any color.
• WWizards of the Coast2013-09-15
  Official Ruling
  Mana symbols in the text boxes of permanents you control don't count toward your devotion to any color.
• WWizards of the Coast2013-09-15
  Official Ruling
  If an activated ability or triggered ability has an effect that depends on your devotion to a color, you count the number of mana symbols of that color among the mana costs of permanents you control as the ability resolves. The permanent with that ability will be counted if it's still on the battlefield at that time.
• WWizards of the Coast2014-02-01
  Official Ruling
  The value of X is calculated only once, as the ability resolves.
• WWizards of the Coast2020-11-10
  Official Ruling
  The type-changing ability that can make Xenagos not be a creature functions only on the battlefield. It's always a creature card in other zones, regardless of your devotion to red and green. It's always a creature spell while it's on the stack.
• WWizards of the Coast2020-11-10
  Official Ruling
  When Xenagos enters the battlefield, your devotion to red and green will determine if a creature entered the battlefield or not for abilities that trigger whenever a creature enters the battlefield. The mana symbols in Xenagos's own mana cost are counted when determining this.
• WWizards of the Coast2020-11-10
  Official Ruling
  If Xenagos is attacking or blocking and it stops being a creature, it will be removed from combat. It won't rejoin combat if it resumes being a creature later during that combat.
• WWizards of the Coast2020-11-10
  Official Ruling
  Counters put on Xenagos remain on it while it's not a creature, even if they have no effect.
• WWizards of the Coast2020-11-10
  Official Ruling
  If an effect causes Xenagos to lose all abilities, its ability that causes it to stop being a creature still applies if appropriate.
• WWizards of the Coast2020-11-10
  Official Ruling
  Xenagos's abilities function as long as it's on the battlefield, regardless of whether it's a creature.
• WWizards of the Coast2020-11-10
  Official Ruling
  If Xenagos stops being a creature, it loses the type creature and the creature type God. It continues to be a legendary enchantment.
• WWizards of the Coast2020-11-10
  Official Ruling
  Your devotion to two colors is the number of mana symbols among mana costs of permanents you control that are the first color, the second, or both. If an effect counts your devotion to two colors, a hybrid symbol that is both of those colors is counted just once.
• WWizards of the Coast2020-11-10
  Official Ruling
  As Xenagos enters the battlefield, your devotion to red and green will determine whether any replacement effects that affect creatures entering the battlefield apply. Because replacement effects are considered before Xenagos is on the battlefield, the mana symbols in its mana cost won't be counted when determining this.

Rulings via Scryfall