Bubbles and Antibubbles
Nope, they aren’t exotic matter that can decimate a entire block when they come in contact with ordinary matter.
Ordinarily, a bubble is air or a sphere of gas surrounded by a thin layer of water. Antibubbles, as the name suggests, is literally the opposite. They are a sphere of water surrounded by a layer of gas and they either float across a body of water or they appear completely submerged underwater.
Check out this fun video about antibubbles from Physics Girl.
Source: Physics Girl. “What are antibubbles?”. YouTube. Published on Aug 2, 2016.