Sure, 5 mana isnt an amazing rate for a board wipe, but it is definitely still acceptable for most Commander decks outside of cEDH
Even so, Gong's defense managed to withstand all of the attacks of "Rune-Eyes" and allowed him to set himself up for a win on the next turn
it gains this effect while face-up on the field: *Once per turn, during your opponent's Standby Phase: Inflict 200 damage to your opponent for each face-down card they control
If it is face-up, negate it's effects and banish it
This is because Knightmare Phoenix can destroy a Spell or Trap without having to be drawn directly from the deck
It isnt a brainless damage machine, you have to plan around when to drop it and when to hit with it, but thats part of what makes pulling and playing it so satisfying