She was a slender pale green. Her horns, crest and wingbones were pearl. At the beginning of the Dance of the Dragons she was considered not quite large enough to bear the weight of Baela Targaryen. When she flew up with Baela to meet Aegon II and Sunfyre she was no larger than a warhorse and weighed less. She was very quick.
She may have hatched from a clutch of eggs produced by Syrax.
Towards the end of the civil war, as Dragonstone fell to Aegon II, Baela was able to escape from her bedchambers as the door was being smashed down. She managed to reach Moondancer in the stable where the castle dragons were kept. There she loosed her chains and strapped a saddle onto her. As Aegon II flew Sunfyre over Dragonmont’s smoking peak up to meet him rose Baela on Moondancer.
The two dragons fought fiercely in the air and eventually fell to the ground, slamming into the hard stone still fighting. Moondancer's quickness proved of little use against Sunfyer’s size and weight and the green dragon soon lay still. King Aegon leapt from the saddle when the dragons were twenty feet from the ground but Lady Baela stayed with her dragon wall the way down. Despite being burned and battered Baela found the strength to undo Moondancer’s saddle and chains and crawl away as her dragon coiled into her death throes. Moondancer was devoured by Sunfyre.