Sacrificial Altar

Sacrificial Altar is an unlockable activated item added in The Binding of Isaac: Afterbirth †.

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.
 * If the Devil Room pool has no items left, one or two copies of 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 effect for a few seconds.

Synergies

 * : 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.
 * / / : 2 Black Hearts will also drop.
 * : Can remove the Isaac's Heart familiar while the item remains, making Isaac invulnerable.
 * : Summoned familiars can be sacrificed since they persist for the entire floor, even without holding the item.
 * : 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.
 * : 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

 * : Cannot be sacrificed in itself, but Locusts can be sacrificed for one coin each, much like Blue Flies.
 * : Locusts created from Abyss are counted as familiars and can be sacrificed as normal.
 * / : 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.
 * / / Eve's Bird Foot / : These familiars can be sacrificed only when they're active.
 * : Converts each Wisp into a Half Red Heart. Spawns a red Wisp and a black Wisp after the sacrifice.
 * / / Umbilical Cord: The familiars generated by these items can be sacrificed and turned into items.
 * : No effect; only spawns one item per familiar sacrificed, and can only sacrifice up to 2 familiars.
 * : The Altar ignores the effects of Chaos, always spawning items from the Devil Room pool instead of a random pool.
 * Conjoined: The transformation will be lost if Isaac has less than three items needed after using Sacrificial Altar.
 * : Each Dip spawned by Dirty Mind is turned into a coin, regardless of type.
 * : Converts all micro-Isaacs into one coin each upon use.
 * : The Intruder can be sacrificed even while it's in Isaac's head.
 * : Created familiars can be sacrificed. Additionally, converts each ghost into a Half Soul Heart.
 * : 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.
 * : 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 item will be lost, and each spawned familiar counts as one sacrifice.
 * : 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.
 * : Each Clot spawned by Sumptorium is turned into a coin, regardless of type.
 * The Twins: Copied familiar cannot be sacrificed, and will disappear with the original familiar.
 * : A Gemini familiar granted by Zodiac can be sacrificed without losing the item.

No effect
The following familiars, followers, and orbitals cannot be sacrificed: 
 * Found Soul
 * Mom's Toenail
 * Tonsil
 * Found Soul
 * Mom's Toenail
 * Tonsil
 * Found Soul
 * Mom's Toenail
 * Tonsil
 * Found Soul
 * Mom's Toenail
 * Tonsil
 * Found Soul
 * Mom's Toenail
 * Tonsil
 * Mom's Toenail
 * Tonsil
 * Mom's Toenail
 * Tonsil
 * Mom's Toenail
 * Tonsil
 * Mom's Toenail
 * Tonsil
 * Mom's Toenail
 * Tonsil
 * Mom's Toenail
 * Tonsil
 * Mom's Toenail
 * Tonsil
 * Mom's Toenail
 * Tonsil
 * Tonsil
 * Tonsil
 * Tonsil
 * Tonsil
 * Tonsil
 * Tonsil
 * Tonsil
 * Tonsil
 * Tonsil
 * Tonsil
 * Tonsil
 * Tonsil
 * Tonsil
 * Tonsil
 * Tonsil
 * Tonsil

Trivia

 * Sacrificial Altar was added in Booster Pack, after the initial release of the DLC.
 * Sacrificial Altar is based on this Steam Workshop item by Niro and PJJLegend, originally known as Satanic Ritual.