Time Wraiths

A Time Wraith is, according to Eobard Thawne, a being connected with Speed Force that appears when a speedster travels through time to stop them from changing history. Its' existance is commonly known to speedsters..

Biography
It appeared to Barry Allen, when he traveled through time to learn how to go faster from his former mentor, Eobard Thawne. When Barry started to impersonate his former self, Wraith came to Central City Police Department looking for him, drawing attention of the officers, including Joe West and Eddie Thawne. Later it visited S.T.A.R. Labs and encountered Caitlin Snow, Cisco Ramon and Hartley Rathaway trying to attack them. Hartley succeeded in finding frequency which, using Sonic Gloves, was able to hurt him. It forced the Wraith to escape.

Later it struck again, when Barry was using The Pipeline in gaining speed to return to his timeline. It almost got him, but past Barry hit him, which slowed him down. Wraith followed after The Flash to his timeline, brought him down and started to suck life out of him, but reformed Hartley stepped in. His attack caused Wraith to explode. It's unknown if Time Wraith was destroyed for good.

Trivia

 * Despite hating time travelers, they have yet to appear on Legends of Tomorrow. This may be due to the fact that they only hunt speedsters who time travel.
 * The creature bears striking resemblance, both in appearance, role and nature, to the Black Flash from the comics, who served as a Grim Reaper to speedsters, especially those who time travel.
 * Its appearance also bears resemblance to the Dementors from Harry Potter.
 * Cisco Ramon once called the creature Inky, a cyan/blue colored ghost from Pac-Man.