Like most Magic: The Gathering cards, the value of Xenagos, the Reveler depends on a few consistent factors: its rarity, the printing and finish (regular or foil), its physical condition, and the set it was printed in (Theros)
Remember that you are not forced to play three or four copies of the same card
The best way to combat this is often with stax pieces
It is also the Creature in Magic: The Gathering with the highest possible power on its own, without infinite combos, which is nothing to scoff at for a game that has been around for over 30 years
The MTG MDFC Rules Change Previously, a modal double-faced card couldnt transform, but that rule is going away
Due to how generic Arven is, almost every deck will have a place for it in the lineup