Pluto

Pluto is a passive item added in The Binding of Isaac: Repentance.

Effects

+0.7 tears
Significantly shrinks Isaac, allowing him to squeeze between objects and makes some enemy shots pass over him.

With enough speed and the correct angle or being pushed by an explosion, it is possible to cross pits and pass through obstacles, allowing Isaac to reach places he usually isn't able to reach.
Pluto can stack with other size reduction effects.
May allow Isaac to squeeze through the walls and floors in Crawl Spaces and 2nd/3rd phase of Rotgut. Passing through the outermost wall in an unintended direction leads to the I AM ERROR room.
The decrease in size makes dodging certain tear effects easier, most notably Hush's continuum tears, and Dogma's feather attacks from their respective second phases.

Cricket's Body: Split tears' range is dropped drastically. Range ups do not mitigate the effect.
Dr. Fetus: Drops the bombs' range drastically despite no change in the range stat, greatly increasing chance of self-damage. Range ups do not mitigate the effect.

Pluto originates from the Antibirth mod. In Antibirth, it would also give a range down.
Pluto's effects reference the planetoid Pluto's nature as a dwarf planet.