This is an Astral Pack foil upgrade waiting to happen.
Grand Horn of Heaven will probably wind up being one of the most-played cards from Dimension of Chaos. Useful against Synchros, Xyz, and inherent Special Summons, its strength lies in its ability to stop the Summon of one monster at a time, or multiple monsters Summoned at once. When you activate Grand Horn against a Synchro or Xyz Summon your opponent loses two cards, you lose one, and then your opponent gains a card – essentially an even two-for-two of card economy. That's not bad.#####CARDID=19161#####
But Pendulum Summoning is the reason Grand Horn of Heaven gets the Spotlight treatment this week. We're standing at the cusp of a new format where Majespecters, Performage Performapals, and Pendulum Magicians will define the competitive field, and Grand Horn stops all of those strategies in their tracks. Pendulum Summoning presents two fundamental problems: it's hard to defend yourself from several monsters at once, and if you destroy your opponent's Pendulum Monsters they just come back next turn.
Grand Horn solves both problems, destroying everything your opponent Pendulum Summons in one shot, and negating that attempted Summon to send their cards to the graveyard instead of the Extra Deck. And while you give your opponent a free card in the process, you shatter their infrastructure and force them to rebuild instead of letting them hammer you again next turn. Meanwhile you're free to press your advantage with your own attacks against what might be an empty field.
That alone would be worth the price of admission, but the fact that Grand Horn can also end your opponent's Main Phase 1 or 2 makes it even crazier. Stop your opponent in Main Phase 1 with a blank field and they probably can't attack you. Shut them down in Main Phase 2 and you push them right into their End Phase, forcing your opponent to set cards and make other Summons before they try for their Special Summon. If they don't play carefully they'll lose the chance to make important moves and leave themselves wide open.
Jump on the bandwagon now, because at the moment, lots of players are unaware of the greatness of this card. I don't think it's going to remain a hidden gem for much longer.