Cult of ThornEdit
The Cult of Thorn was a cult of druids. Although depending on which version seen of Halloween 6, There are some differences. In the Official verison, the Sanitarium crew have grown more interested in harvesting and exploitng the power of Thorn through DNA; becoming merely cult geneticists relating the rune of Thorn to modern science and using Michael's DNA during their own experiments. The Sanitarium has been using the women of the institution for their experiments by possibly performing in vitro fertilization on them with embryos artificially inheriting Michael's DNA.
In the "Producer's Cut" of Halloween 6 they are actually the "Cult of Thorn".
Curse of ThornEdit
The Curse of Thorn is a constellation that could appear during Halloween. To prevent mass death among the tribes, one family was chosen to bear the curse. This curse would require the bearer to sacrificially murder his or her entire family, which in turn would spare their community from events such as plague and drought. The curse also appears to give the cursed inhuman strength and immunity from death.
The curse was greatly explored in the "Producer's Cut" of Halloween 6, with more importance given to Dr. Wynn and his Cult. At the end of that cut, a dying Wynn passes the curse to Dr. Loomis which is the real reason Loomis screams at the end of the film.