The Hexproof deck suits up one of its trademark untargetable dorks and the opponent simply didnt get to play Magic as he or she got attacked to death by a 9/9 Trample, Lifelink, First Strike, Hexproof Creature
Then if you transform
This is a quick effect, meaning if you activate this card during the damage step, your opponent is gonna take some serious damage (and not even see it coming)
Even if "Fire King High Avatar Garunix" is destroyed by battle, you can Special Summon another "Fire King" monster from your Deck, so you can always have monsters on your field once you Summon this monster
But at the end of the day, it's always going to have value because this is a game about creatures attacking and blocking, and this will do so very nicely, either as a 4/4 flying haste-ed one, or just a 5/5 flying that can also shoot stuff if properly en-countered (say, by putting the counter on and not immediately swinging)
A Liliana, the Last Hope ultimate or Raging Ravine will get the job done once they are completely attritioned out
