The Ur-Dragon Dragon ambush We like Scion of the Ur-Dragon a lot, but if you dont mind ramping up a bit more, The Ur-Dragon is incredibly mighty as a MTG commander
But, in the end, they were cut to make space for other mechanics
Braingeyser will let you refill your hand as needed at this point, and you should be able to generate infinite mana, infinite Shivan Dragons, or the opportunity to fire off infinite Braingeysers at your opponents
Youre rewarded not just for stuffing your deck full of black-green squirrels, for example, but also for foraging with food tokens and graveyards
I mean, I can understand that somewhere, someone designed this card thinking that often you would add X mana to your pool and not be able to use it, with mana burn ensuing
Nest of the Hydra may generate a vanilla creature, but is about the best mana sink a Green deck could ask for