Sacrificial Altar 
Effects
- Upon use, sacrifices up to 2 familiars and spawns an item from the Devil Room pool for each familiar sacrificed.
- The order in which the familiars were obtained does not matter; it picks 2 at random to sacrifice.
- If Isaac has no familiars, no Blue Flies, and no Blue Spiders, the item will do nothing and will not be consumed.
- Even if Isaac doesn't have any familiars, if he has a single fly, spider, or locust, the item will be consumed.
- If the Devil Room pool has no items left, one or two copies of
Pentagram are spawned.
- When playing Greed Mode, the normal Devil Room pool is still used, instead of the Greed mode pool.
- In addition to the familiars, any Blue Flies, Blue Spiders, or Locusts will be converted to 1 Penny each.
- On use, causes a brief (Curse of Darkness.png) Curse of Darkness effect for a few seconds.
Notes
Synergies
- (Added in Repentance)
Book of Virtues: Converts each Wisp into a (Half Red Heart) Half Red Heart. Spawns a red Wisp and a black Wisp after the sacrifice.
- (Removed in Repentance)
Brown Nugget: Spawned fly turrets count as familiars for sacrificing; although dropping the Brown Nugget will despawn the last fly turret, older ones will remain and can be sacrificed.
- (Added in Repentance) Spawned fly turrets count as regular blue flies for sacrificing, and thus are converted to pennies.
Guardian Angel / 
Seraphim / 
Sworn Protector: 2 Black Hearts will also drop.- (Removed in Repentance)
Isaac's Heart: Can remove the Isaac's Heart familiar while the item remains, making Isaac invulnerable.
- (Added in Repentance)
Monster Manual: Summoned familiars can be sacrificed since they persist for the entire floor, even without holding the item.
- (Added in Repentance)
Plum Flute: Using Plum Flute, then using Sacrificial Altar will remove the Baby Plum spawned and spawn an item. The Plum Flute is not removed upon doing this, and subsequent usage of Plum Flute still summons Baby Plum normally.
- (Added in Repentance)(The Twins) The Twins: Both the duplicated familiar (if one is available) and Brother Bobby/Sister Maggy (if not available) can be sacrificed for an item reward. This does not remove the trinket, and fully retains its effect.
- (Removed in Repentance)
Void: When absorbed by Void, the one time use no longer applies, unlike other one time use active items. Familiars can be sacrificed with every activation of Void.
Interactions
- (Removed in Repentance)
7 Seals: Cannot be sacrificed in itself, but Locusts can be sacrificed for one coin each, much like Blue Flies.
- (Added in Repentance)
Abyss: Locusts created from Abyss are counted as familiars and can be sacrificed as normal.
Ball of Bandages / 
Cube of Meat : The altar consumes the whole familiar, up to 4 cubes or balls at a time. If more than 4 are available, they count as other familiar(s) that may be separately chosen for sacrifice.
Best Bud / 
Dead Bird / (Eve's Bird Foot) Eve's Bird Foot / (Added in Repentance)
Bird Cage: These familiars can be sacrificed only when they're active.
Box of Friends / Monster Manual / (Umbilical Cord) Umbilical Cord: The familiars generated by these items can be sacrificed and turned into items.
Car Battery: No effect; only spawns one item per familiar sacrificed, and can only sacrifice up to 2 familiars.
Chaos: The Altar ignores the effects of Chaos, always spawning items from the Devil Room pool instead of a random pool.- (Added in Repentance) (Conjoined) Conjoined: The transformation will be lost if Isaac has less than three items needed after using Sacrificial Altar.
- (Added in Repentance)
Dirty Mind: Each Dip spawned by Dirty Mind is turned into a coin, regardless of type.
- (Added in Repentance)
Giant Cell: Converts all micro-Isaacs into one coin each upon use.
Halo of Flies: Both flies created by this item are counted as a single sacrifice each, due to the fact that they are counted as pretty flies.- (Added in Repentance)
The Intruder: The Intruder can be sacrificed even while it's in Isaac's head.
- (Added in Repentance)
Lemegeton: Created familiars can be sacrificed. Additionally, converts each wisp into a (Half Soul Heart) Half Soul Heart. The passive item effects granted by the familiars is retained for the duration of the floor.
- (Removed in Repentance)
Lil Delirium: Lil Delirium may be sacrificed, but the item is not removed. The familiar will return once another familiar is gained or lost, or the run is quit and resumed.
The Pinking Shears: Body familiars that are spawned by this item can be sacrificed by switching between the Pinking Shears and Sacrificial Altar. (Removed in Repentance) However, the body familiars reappear when picking one of the spawned items up.- (Added in Repentance)
Quints: The item will be lost, and each spawned familiar counts as one sacrifice. If Quints is sacrificed first (or is the only item available to sacrifice) and at least two familiars are summoned, two Devil Room items will be spawned while only losing one item.
- (Added in Repentance)
Star of Bethlehem: Although not readily apparent as a familiar, the Star can be sacrificed. It will be destroyed even if it is not currently in the same room.
- (Added in Repentance)
Sumptorium: Each Clot spawned by Sumptorium is turned into a coin, regardless of type.
Zodiac: A Gemini familiar granted by Zodiac can be sacrificed without losing the item.
Incubus familiar cannot be sacrificed.