Sacrificial Altar

Sacrificial Altar is an unlockable activated item added in The Binding of Isaac: Afterbirth † (Booster Pack #5).

Effects

Upon use, sacrifices up to two familiars and spawns an item pedestal for each familiar sacrificed.
- The order in which the familiars were obtained does not matter; it picks 2 at random to sacrifice.
Any Blue Flies, Blue Spiders, Locusts, Clots, Dips, or Minisaacs will be converted to 1 Penny each.
Wisps will be turned into Half Red Hearts each, and Item Wisps will be turned into Half Soul Hearts.

The list of possible item rewards include:

If Isaac already has all of the above items, copies of Pentagram will replace any further items spawned.
On use, causes a brief Curse of Darkness effect for a few seconds.
If Isaac has no familiars of any kind, including any temporary familiars, the item will do nothing and will not be consumed.

Notes

If playing as Lilith, the Incubus familiar cannot be sacrificed.
- Other starting familiars, such as those granted by Eden's Blessing or a challenge, can be sacrificed as normal.
Charmed and friendly enemies cannot be sacrificed.
Any Pretty Flies are counted as a single sacrifice.
Familiars spawned from Trinkets like Isaac's Head can be sacrificed, destroying the trinket in the process.
Upon use may remove Transformations.

Synergies

The Book of Belial + Birthright as Judas / Dark Judas: Grants +10.8 temporary damage up for every sacrificed familiar. The damage bonus scales down to 0 over time, similarly to Red Stew. Sacrificing blue flies or blue spiders has no special effect.
Book of Virtues: Converts each wisp into a Half Red Heart. Spawns a single red and black wisp in the middle ring after the sacrifice.
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.
- Spawned fly turrets count as regular blue flies for sacrificing, and thus are converted to pennies.
Cambion Conception / Immaculate Conception: Familiars can be sacrificed without consuming the item. The sacrificed familiars will also respawn upon entering a room.
Guardian Angel / Seraphim / Sworn Protector: 2 Black Hearts will also drop.
Isaac's Heart: Can remove the Isaac's Heart familiar while the item remains, making Isaac invulnerable.
Lemegeton: Created familiars can be sacrificed. Additionally, converts each wisp into a Half Soul Heart. The passive item effects granted by the familiars is retained for the duration of the floor.
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.
Quints: The item will be lost only if Isaac has at least 1 spawned familiar in the room used, 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.
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.
Pretty Fly Horse Pill: Sacrificing the Big Fan spawned by the pill gives Isaac two Pretty Flies.

Interactions

7 Seals: Cannot be sacrificed in itself, but Locusts can be sacrificed.
- Can now be sacrificed as usual.
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 / Bird Cage: These familiars can be sacrificed only when they're active.
Box of Friends / Monster Manual / Umbilical Cord / The Twins / Soul of Lilith: The familiars generated by these items can be sacrificed and turned into items.
Car Battery: No effect.
Chaos: The Altar ignores the effects of Chaos, always spawning items from its usual drop pool instead of a random pool.
Conjoined: The transformation will be lost if Isaac has less than three items needed after using Sacrificial Altar.
Dirty Mind / Dingle Berry: Each Dip spawned by these items or from a Charming Poop is turned into a coin, regardless of type.
Giant Cell: Converts all Minisaacs into one coin each.
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. The item is taken away if either of the flies are sacrificed.
The Intruder: The Intruder can be sacrificed even while it's in Isaac's head.
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. However, the body familiars reappear when picking one of the spawned items up.
The Swarm: Each fly will be turned into a coin without consuming the item.
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.
Sumptorium / Lil Clot: Each Clot is turned into a coin, regardless of type.
Super Bum: Super Bum may be sacrificed, but none of the items will be removed. The familiar will return once another familiar is gained or lost, or the run is quit and resumed.
- Super Bum may be sacrificed but only one of the items will be removed.
Vengeful Spirit: Wisps will be sacrificed for one coin each.
Zodiac: The Gemini familiar granted by Zodiac can be sacrificed without consuming the item.

No effect

The following familiars, followers, and orbitals cannot be sacrificed:

In-game Footage

Trivia

Sacrificial Altar is based on this Steam Workshop item by Niro and PJJLegend, originally known as Satanic Ritual.
Unlike costumes from other active items, Sacrificial Altar's costume is permanent after it is used,