"Sacrificial insemination" Item ID
Collection Grid (page 5, column 14, row 3) (page 5, column 15, row 3) Unlock Method
Spawn three charmed enemies in the same room
Mystery Egg is an unlockable passive item added in Booster Pack #5.
Spawns an egg familiar, which cracks and turns into a random friendly enemy when Isaac is hurt.
The egg regenerates upon entering a different room.
The usefulness of the enemy depends on how many rooms have been cleared without getting hurt.
The list of available monsters is as follows:
Number of rooms / waves cleared
0 to 1 rooms cleared without taking damage
Black Fly, Attack Fly, Maggot, Spider, Dip, Embryo, Nerve Ending
2 to 4 rooms cleared without taking damage
Moter, Pooter, Swarm Fly, Level 2 Fly, Full Fly, Horf, Sucker, Dart Fly, Big Spider, Guts, Hopper, Gusher, Round Worm, Heart, Gush
5 to 7 rooms cleared without taking damage
Squirt, Ragling, Homunculus, Level 2 Spider, Small Baby Long Legs, Wall Creep, Nightcrawler, Ulcer, Ministro, Mulligan, Hive, Nest, Flaming Hopper, Gaper, Cyclopia, Skinny, Dople, Globin, Maw, Psychic Horf, Tumor, Fatty, Half Sack, Clotty, Charger, Brain, Conjoined Spitty, Buttlicker, Host, One Tooth, Baby, Dukie, Black Globin's Body, Black Globin's Head, Para-Bite
8 to 10 rooms cleared without taking damage
Splasher, Boom Fly, Keeper, Fat Bat, Psy Tumor, Imp, Fred, Cod Worm, Lump, Swinger, Bony, Black Globin, Null, Begotten, Knight, Bone Knight, Blubber, Conjoined Fatty, Oob, Leech, MemBrain, Wizoob, Mr. Maw, Flesh Death's Head, Mushroom, Blind Creep, The Thing, Blister, Leaper, Hanger, Poison Mind, Fistuloid, Tar Boy
11 to 13 rooms cleared without taking damage
Gurgle, Walking Gut, Black Bony, Black Maw, Camillo Jr., Eye, Roundy, Mom's Hand, Mega Clotty, Swarmer, Fat Sack, Mobile Host
More than 13 rooms cleared without taking damage
Red Ghost, Rage Creep, Vis, Gurglings, Dinga, Portal
: The enemy spawned will be a champion variant and egg grows in size.
BFFS! Even if the enemy spawned cannot be a champion under normal circumstances, they will become a champion. For example, a spawned Dip can become a Red champion while a Round Worm can become a Green champion.
: Losing the Mantle will not cause a friendly enemy to spawn. Holy Mantle
When using with Mystery Egg, after the egg turns into a friendly enemy, the electricity shoots out into a random corner of the room.
When egg turns into a friendly Heart ( Mask + Heart) will sometimes act as the heart companion for a mask already in the room resulting in an unbeatable room.
Mystery Egg's familiar appearance.