This card cannot be Normal Summoned or Set. This card cannot be Special Summoned except by the effect of "Bonding - H2O". While this card is face-up on the field, the ATK of FIRE monsters and Pyro-Type monsters become 0. When this card is destroyed and sent to the Graveyard, you can Special Summon 2 "Hydrogeddons" and 1 "Oxygeddon" from your Graveyard.
Using Diamond Dude's effect, you can special summon Water Dragon without having to summon Hydrogeddon, or Oxygeddon on to the field. You don't even have to bring the monsters in the deck since you it can activate without the cost.
You can change your opponent monster's attribute into Fire so that their attack will become 0, allowing you to deal damage like a direct attack. But using DNA Transplant will also reduce its own attack, which can be good if you want to crash into your opponent, or simply just special summon Water Dragon in defense position.
Literally no reason to ever have more than one copy of this card. It can be summoned from anywhere and it's impossible to summon more than one to the field under the normal method (since you can't have four monsters on the field). Diamond Dude can give you more than one, I guess...but then you increase the risk of dead draws.
You're right, Matt. The idea then becomes to keep only 1 monster on both sides of the field, kamikaze w/ Water Dragon, and sweep with his revived components. Between that field condition and his bizarre summoning condition, he's gonna be impractical at best, as always.
if this card can counter the fucking nepthys then GX is welcomed