Entity 66, a culmination of Frisk and the six human souls, came into existence when the core had a meltdown and destroyed half the underground. It was shattered across reality, but is slowly reforming and gaining power.
Entity 66 is a human child with grey skin, dark grey hair, and Frisk's clothes. It has grey eyes.
Entity 66 rarely gets into conflict, and when it does it is probably trying to stop disaster from coming. It travels from universe to universe keeping the fabric of reality intact.
Entity 66's level is constantly growing, and so are it's stats. It has the Core Knife and the Core Locket equipped, which both give 999 ATK/DEF.
Entity 66 can summon various types of magic, from all soul types. It can also summon grey magic, or void magic.
Entity 66 has made many friends and enemies in varios AUs, but the most notable are Core!Gaster and Core!Sans.
Entity 66 is good friends with Core!Gaster. They agree on many things, and work together to restore themselves to thier former state.
Unlike Core!Gaster, Core!Sans hates Entity 66. The reason for this is unknown.