The legendary Intimidated Outlines, originally developed by Undeadsewer, updated for U219.4

unsynced means: This version will not send any network code about the outlines to other clients at all. - The outlines are local only.

Most other Intimidated Outlines mods usually tried to sync the outline to others, which caused alot of problems for everyone.
This one is safe to use. atleast for others, it might only blow up your own machine.
Stay safe, clowns!