The spells last 2 hours and there's a 20 hour real time timer on using the device. The weapon spells do not stack with minor/major item spells. The attribute spells do not stack with creature self spells or beers.
The timer is shared by all three variations of the Black Spear.
During the The Quest for Freedom event the Black Spears timer was mistakenly set from 20 hours to 27 days.
You must wait 26d 23h 59m 59s before you can use the Black Spear again.
During the Shattered Masks event the Black Spears timer was reset back to 24 hours.
The Black Spear seems to writhe in pain like a snake for a moment, then it casts on you.
Black Spear of Mukkir Strength cast Strength Other Incantation on you.
Black Spear of Mukkir Strength cast Coordination Other Incantation on you.
Black Spear of Mukkir Strength cast Focus Other Incantation on you.
Black Spear of Mukkir Strength cast Mukkir Sense on your (weapon/caster).
Black Spear of Mukkir Strength cast Mukkir's Ferocity on your (weapon/caster).
You have used one of the Black Spears already. You must wait 19h 59m 37s before you can use the Black Spear again.