Originally posted by Karl Green:
• Slow Casting time (double the time required) lower the DC by 2
• Fast Casting time (half the time required) increase the DC by 5
• Sacred Space (temples, medicine lodge, holy ground, etc) specific to the ritual performed but generally lower or increase the DC by 1-5
• Material Components (occults symbols of power, magic circles, sacrificial offerings) specific to the ritual performed but generally lower or increase (some Rituals require them to be cast) the DC by 1-3
• Additional Casters generally lower the DC by 1 or 2