The Intruder is a passive item.
- A familiar burrows in Isaac's head, firing four slowing tears in addition to Isaac's normal tears.
- These tears are unaffected by Isaac's damage and tears stats; they have fixed damage and fire rate.
- Upon taking damage, there is a chance that Isaac's head will pop, spawning friendly spiders, and release the Intruder familiar.
- It will leap at enemies to deal contact damage as a Trite does, and frequently fires four slowing tears towards nearby enemies.
- The familiar only lasts for the current room, and Isaac's head is reattached upon entering a new room.
- Once picked up, The Intruder cannot be rerolled by any means, similar to Key Piece 1, Key Piece 2, or any of the Knife Pieces.
- The Intruder is treated as a familiar even while in Isaac's head, and benefits from familiar synergies.
- Brimstone: If Isaac's head pops off, it will be impossible to determine if Brimstone has been fully charged or not.
- Transcendence: If Isaac's head pops off, Isaac will be invisible for the rest of the room aside from a shadow and orbitals.
- Song of the Siren (trinket): Will roughly double the fire rate of the spider's tears, even while it resides inside Isaac's head.
- The appearance of this item on Isaac is possibly a reference to the Hellbenders pilot (Zachnaphobia), in which the character "Zach" is controlled by a parasitic spider.
VLQZ E94W (First floor treasure room)