Darkgold Dragon

[DynamicSoldier]

2 Level 4 monsters

Once per turn, when this attacking card destroys an opponent's monster by battle and sends it to the Graveyard: You can detach 2 Xyz Materials from this card; Special Summon the destroyed monster to your opponent's side of the field in face-up Attack Position, also its ATK becomes half its current ATK, and if you do Summon this way, this card can make a second attack during this Battle Phase, and if it does, this card gains that lost ATK.

[Trebuchet MS]

From what I see, it's a mish-mash of Shark Drake and Dark Rebellion Xyz Dragon.

 

Needing to score a kill in battle reduces the scope of what it can effectively work on, but once it goes off, you get an additional near-guaranteed 2500 damage and a significantly larger monster. Sometimes it may end games. Other times it becomes a not-so-viable option if you're standing against several monsters with sizable stats.

 

Personally prefer Dark Rebellion Xyz Dragon over this card since DRXD can almost automatically grow to a humongous curb-stomping size without needing an attack prior to that. Doesn't mean that Darkgold Dragon is bad. Just that it has very close competitors.

[Hello my name is Enguin]

So it's DRXD that has to kill something to get its effect and is as a result not nearly as good. Only realised now that it summons it back to your opponent's field not yours, well that makes it even less useful then. Can't see any scenario where you'd want to go for this and risk not even getting the boost. It's susceptible to all kinds of things that don't matter to DRXD, chief among them monsters with more than 2500 ATK in the first place.

[Mugendramon]

DRXD is better because it lets you overpower two monsters where this only ever gets one and even then it has to be under 2500.