Isaac wears Monstro's Tooth as a necklace.
Upon activation, Monstro will jump down from above and land on a random enemy, if any. If there are none, Monstro will aim for Isaac himself.
- To meet the Unlock condition, the following bosses must be killed at least once:
- You can damage and kill the spawned Monstro if you're quick enough (i.e. freezing him or let him land into Satan's laser), but he won't drop anything.
- The summoned Monstro can also be an alternatively coloured champion version instead of the normal coloured version.
- Champion versions cause additional effects (ie, red triggers moms foot to strike area after short delay)
- This item cannot be used on a fight against Monstro, but can be used on Monstro II.
- If used on War when he drops troll bombs, War will become stuck and the player will have to restart the game.
- In Rebirth, Monstro's Tooth has a sizeable crack in it.