Wikia

Ghost Dragon
Adult Adult - Juvenile Juvenile - Baby Baby - Egg Egg		Available	Level 9
		Buy	75
		Sell	15,000
		EXP	7,500
		Breeding Times	15 Hours 30 Min
		Breeding Times	12 Hours 24 Min
		Incubation Time	15 Hours 30 Min
Habitats	Cold, Earth	Boost
Limited:	EXPIRED	Boost
Game Description
Often mistaken as the spirit of an ancient and benevolent dragon, the ghost dragon remains somewhat of a mystery. Reading the notes of the wizard Sam Hain, "The ghost dragon only shows up in the middle of the Fall, usually in conjunction with the bone dragon. My advice? Don't be afraid of no ghosts!"

Breeding

Coin per minute:

Lvl. 1	Lvl. 2	Lvl. 3	Lvl. 4	Lvl. 5	Lvl. 6	Lvl. 7	Lvl. 8	Lvl. 9	Lvl. 10
6	10	13	17	20	24	28	31	35	38
Lvl. 11	Lvl. 12	Lvl. 13	Lvl. 14	Lvl. 15	Lvl. 16	Lvl. 17	Lvl. 18	Lvl. 19	Lvl. 20
42	46	50	53	57	60	64	67	71	75

Dragon Earning Rates without boosts.

Boost Calculation Guide to use with the page linked above.

Release	Removal
October 18, 2012	November 5, 2012
December 18, 2012	January 14, 2013

The Ghost Dragon's combined breeding/incubation time may be related to the date of Halloween, as 15.5 + 15.5 = 31.
The name Sam Hain likely refers to Samhain. Samhain (pronounced "sow-en") is a Gaelic festival marking the end of the harvest season and the beginning of winter or the 'darker half' of the year. Most commonly it is held on October 31 October - November 1, or halfway between the autumn equinox and the winter solstice.
The phrase "Don't be afraid of no ghosts!" most likely refers to a line from the theme song of the movie "Ghostbusters": "I ain't afraid of no ghost!"