From A Wiki of Ice and Fire
A Feast for Crows
It was brought to the Kingsmoot by Euron Greyjoy when the ironborn were electing a new king. The horn's noise silenced all and ended the possible fight between the supporters of Victarion and Asha Greyjoy.
The horn's noise according to witnesses sounded like the screaming of a thousand souls and made it seem to the listeners as if their very bones were aflame and searing there very flesh from within .Cragorn the man who blew the horn collapsed with blisters on his lips and the tattoo he had of a bird on his chest was bleeding. He died later and when a maester cut him open to examine the cause of death it was discovered his lungs were charred black as soot.
A Dance with Dragons
|“||"I am Dragonbinder, No Mortal man should sound me and live, Blood for Fire, Fire for Blood" ||”|
Moqorro says whoever blows the horn will die but any dragons that hear will obey the horn's master. Moqorro says Victarion must be made the horn's master and he must claim the horn with blood.