Note: This was taken directly from VS Battles. Please give them the credit they deserve.
Density Manipulation is the ability to control the density of objects and beings, possibly including one's self. This power can be used to make objects denser, heavier, and more durable, or to lower their density to become lighter and more agile, or even to make them disperse and lose their solidity. It can potentially be used on one's self to make the user intangible, allowing them to phase through others. It is also associated with Gravity Manipulation and, at high levels, can potentially even be used to create black holes.