Density Control (self) – The ability to increase and/or decrease the natural density of one’s body. Density Control (self) is also known as Personal Density and Self-Density Manipulation.
The Vision (Marvel) can both increase and decrease his own density. In Avengers V1 #166-29, the Vision decreases his mass to fly very high and then increases his mass and density to deliver a blow that takes out Count Nefaria (Marvel).
Dynamo wears a belt that allows his to increase the density of his body as seen in T.H.U.N.D.E.R. Agents #3 (Tower).