Mysterious and altars to petty and lost gods can be found in remote and forgotten places, the spirits involved may still grant boons or banes to those that stand before them.
1-30 any supplicant
31-45 any supplicant speaking proper prayers
46-60 any supplicant of specific alignment
61-70 any supplicant of a specific class only (usually but not always cleric)
71-90 any supplicant making an offering of wealth (wealth disappears in 1-6 turns), 100 gp per level is suggested maximum monetary offering.
91-100 To any supplicant making a sacrifice or a living being. Minimum sacrifice of 1 HD of beings per dungeon level recommended.
Duration of ritual (roll 1d100)
Altar power takes effect:
16-20 after 1-3 rounds
21-50 after 1-4 turns
51-75 after 2-12 turns
76-90 after 1-4 hours.
91-100 after 3-24 hours.
Altar (roll 1d100)
1-15 Healing: supplicant is healed 1d6 damage per 2 dungeon levels, once a day at most.
16-25 Blessing: supplicant is blessed for 12 turns
26-30 Revealing: will identify a magical item placed at it's base, 20% chance it the magical item vanishes.
31-35 Rebirth: will raise a corpse but might simply animate the corpse as an undead monster. The chance of getting an undead monster is 10% + 10% per raised corpse within the past week.
36-40 Contact Other Plane: allows user to contact other plane as per spell.
41-50 Clairvoyance: supplicant gains clairvoyance as spell up to 600' feet away.
51-55 Bloody Offerings: looks like altar of rebirth but consumes corpse.
56-60 Trapped: the altar is trapped (determine traps as normal for dungeon)
61-65 Miracles: if supplicant is spell-caster will regain a 1st or 2nd level spell up to 3 times over the next day.
66-75 Protective: no evil may approach within 60' of altar or commit violence into this space unless attacked from inside the space protected.
76-80 Conversion: any supplicant will be converted to alignment of the altar. A cleric of same alignment can convert one unwilling convert a week who fails a saving throw.
81-95 False Idol: the altar engravings or statuary act as a statue generated on the statue table.
96-100 Altar of Trials: A supplicant to this altar will be cursed. Once they return with three sacrifices or offerings to this altar the curse is removed and there is a 20% chance a random attribute is permanently raised by one point and the supplicant alignment is changed to that of the altar. Attempting to gain another ability point will be (roll 1d6): 1-2 ignored, 3-4 result in permanent curse and no ability point gains, 5-6 result in permanent curse and ability point gained (if this curse is somehow removed ability point is lost)