There are many champion spawns on UO Eventine. Custom and Normal.
Spawning, Facets and Timers
Spawn timers for most champs will be randomized from 4 to 8 hours. They can be resummoned with Valor within 30 minutes of respawning. (meaning if the spawn will spawn within 30 minutes, you can respawn it with valor).
Felucca And Faraan Champion spawns give power scrolls.
Any Seasonal Champion Spawn will give power scrolls.
The rest will give Power Scroll Credits from the Power Scroll Exchange.
Felucca Champion Spawns give 1 scroll to every person. If you do the champ alone you will receive 2.
Faraan Can give up to 6 for soloing, or if 6 or more complete the boss, everyone will get a scroll.
These changes are to help balance out the champion spawn system.