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.
Aw man, in this type of game? Here I thought Destiny Hero Plasma was hard to summon (along with Alexis’s ace fusion monster since you have to use the 2 monsters and only give you one copy of one of those monsters from the start and have to duel Alexis for any more. Who thought this was a good idea?)
To the dragon’s credit, he has his uses like the anti-Phoenix deck. And as hard as he is to summon, there are worse ace cards (I still consider Legendary Fisherman to be the worst, and Harpie Lady Sisters is almost just as bad in my opinion.)
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.