Shackel was a planet that was devastated by the Imperial Remnant during the Galactic Civil War.
Once the planet had cities of glass.
In 5 ABY the planet suffered an by the Imperial Remnant, one of the many during the recent years. After the event, its plains were seen from orbit as heat-fused earth, into which merged the glass rubble that once were its cities.
Soon, a Rebel fleet consisting of the medical frigate Mercy, an antiquated Dreadnaught (possibly the New Hope), two Assault frigates, a squadron of Corellian Gun ships and other support vessels came to its vicinity. The Mercy received six thousand of wounded, overwhelming its wards, corridors and medical staff.
The planet was first mentioned in the audio adaption of the novella Dark Forces: Rebel Agent, which was released in 1997. As the planet's name is only given in spoken dialogue from the audio adaption, the actual spelling cannot be determined.
In the novella the planet and the attack are not mentioned; however the Mercy is seen orbiting an unnamed, recently devastated, planet, strongly suggesting that the casualties seen on board are from there. This article treats them as the same planet. It is also possible that the unnamed planet is Milagro which appears in the sequel novella Dark Forces: Jedi Knight, described as having ruined cities of molten glass and crystal after some attack.