Ritual
Rituals are a map event where a Ritual Altar appears.
After activating the ritual altar you have to fight off a wave of enemies, who give you favor by defeating them; after the fight is over you can spend Tribute (Ritual League) at the ritual altar and pick from a list of various per-identified rares that cost favor.
Rituals have various buffs to enemies and enviromental damage effects listed here
Ritual Modifiers
Infernal
Monsters do increased fire damage and can ignite , and meteors hit the ground that shoot out smaller fireballs that do damage randomly.
Supressive
Monsters regenerate life, Smothering mist reduces health regeneration.
Violent
Monsters do increased physical damage and can cause bleeding, Pain totems pulse damaging waves.
Bitter
Monsters deal extra cold damage and can freeze, Ice beams rotate.
Ensconced
Monseters gain extra energy shield based on life, Altar restores monster energy shield.