The raids happen every tree hours in the 45th minute.
Everyone has an equal chance of killing; all players deal only "1" of damage to raid monsters.
The number of monsters that will be spawned is based on the number of players online.
You can check the loot of raid monsters on Monster Loots.

To check the raids times in game use the command !raids

Monster:	Health:	Cities:
Lucky Elf	70/70	Woodlands, Ab Dendriel,
Lucky Chakoya	70/70	Iceland
Lucky Mummy	70/70	Amarna
Lucky Goblin	70/70	Carlin, Carnifes
Lucky Ghoul	70/70	Ireland
Frost Colossus	100/100	Iceland
Bigfoot	800/800	Iceland

Celestial Key Fragments

One of the most important loot of raid monsters are definetely the celestial key fragments.
With a bunch of them and a little bit of luck you can transform it into a celestial key.

More informations: Go to Carlin and talk to the NPC: Sereno.