- A key hole appears on Isaac's forehead.
- Sets key count to the maximum of 99.
- The "Bombs Are Key" Pills can help Isaac to convert the excess of keys into bombs.
- A skeleton key is a key that has been altered in such a way as to bypass the wards placed inside a warded lock. The term derives from the fact that the key has been reduced to its essential parts.
- The term "skeleton key", in a more general sense, is also sometimes used in reference to key or similar object capable of opening any lock regardless of make or type.