Like most Magic: The Gathering cards, the value of Green Sun's Twilight depends on a few consistent factors: its rarity, the printing and finish (regular or foil), its physical condition, and the set it was printed in (Phyrexia: All Will Be One)
He is a lord who is kind to the non-paying force
The best part of having your Shadowspear or some other equipment attached to Shimmer Dragon is that when it taps to attack - the equipment does not tap with it
Secondly, it destroys anything, which means our test can be used on any permanent
This means that it can knock out a Basic Pokemon with 60 HP in only two turns as opposed to taking three
Outside of that, it triggers on enters the battlefield, so repeated flickering could net you additional cards