Time Wraiths

"That's what we call them. Time Wraiths. Scary, aren't they?"

- Eobard Thawne, about Time Wraiths to Barry Allen

Time Wraiths are, according to Eobard Thawne and Hunter Zolomon, a race of wraith-like beings who are the enforcers of the Speed Force. Since they are enforcers of this energy, they are intimately connected with (and likely live in) the Speed Force. Thawne claimed the only way to draw their attention is by carelessly travelling through time. However, Zolomon revealed that Time Wraiths will also attack anyone who breaks the rules of the Speed Force, calling them "its enforcers". Their existence is common knowledge among speedsters.

Biography
At an unknown time in the past, Eobard Thawne came in contact with Time Wraiths and learned to fear them. Zoom also gained their attention when he began trying to manipulate the Speed Force to counteract the Velocity-9's negative effects on his systems. The Time Wraiths hunted Zoom relentlessly for ages but in due time, they somehow lost track of the demonic speedster.

A Time Wraith appeared to Barry Allen when he traveled through time in order to learn how to increase his speed from his former mentor, Eobard Thawne. When Barry started to impersonate his former self, the Time Wraith came to the CCPD looking for him, drawing the attention of numerous officers, including Joe West and Eddie Thawne. Later, it visited S.T.A.R. Labs and, encountering Caitlin Snow, Cisco Ramon and Hartley Rathaway, tried to attack them. Hartley succeeded in finding a frequency which, using his Sonic Gloves, was able to hurt him. It forced the Wraith to escape.

Later it struck again, when Barry was using the The Pipeline in gaining speed to return to his timeline. It almost got him, but past Barry tackles the creature, giving present Barry the opening to go into the Speed Force. The Wraith then followed The Flash to his timeline, brought him down and started to suck the life out of him, but the reformed Hartley stepped in and used his sonic gloves to obliterate it.

During the race between The Flash and Zoom, Barry created a time remnant, causing two Time Wraiths to be summoned. When they arrived, they surrounded Zoom rather than The Flash and took him away, likely sparing Barry for using the time remnant to save the Multiverse and aiding in Hunter's capture.

Powers

 * Flight: Time Wraiths can fly and hover which is only natural since they do not have legs to walk or run on.
 * Intangibility: Time Wraiths can move through solid objects, like ordinary walls and doors, but cannot penetrate the S.T.A.R. Labs meta-human prison cells.
 * Super speed: Time Wraiths can fly at blindingly fast speeds, enabling them to easily keep up with and catch speedsters, however, being as fast as he was, they couldn't catch Zoom until Barry beat him and handed him off to them.
 * Super strength: Time Wraiths can exert immense physical force, despite their frail appearance; one was able to almost break into an impenetrable Star Labs Pipeline cell and later pin Barry to the ground with one hand. Two of them could effortlessly carry off Zoom into a portal while only holding his arms.
 * Super durability: Time Wraiths cannot be damaged by most physical attacks; so far the only way to damage them is with a sonic attack that uses low frequency with high intensity.
 * Time travel: Time Wraiths are able to follow speedsters anywhere in the timeline.
 * Immortality: Time Wraiths exist in the Speed Force outside the normal flow of time, therefore they can last forever; so far the only way to permanently kill then is with a sonic attack that uses low frequency with high intensity.
 * Life-force draining: Time Wraiths can drain life-force through physical contact, the effect of this has the appearance of greatly accelerated ageing on their victim, which is completely undone if the Wraith loses physical contact with them.
 * Transformation: Time Wraiths are capable of reshaping and altering the appearance and powers of Speedsters like Hunter Zolomon, whom they transformed into a gray, skeletal, demonic-looking figure. They also changed the coloured of his speed force lightning from blue/yellow to red and changed the colours of the lightning-bolt emblem on his suit.

Weaknesses

 * Frequency attacks: Time Wraiths are can be hurt and given pain by sonic frequencies, but can only be destroyed by low frequency-based attacks with higher intensity, which could be made by devices such as Hartley Rathaway's sonic gauntlets.

Behind the scenes

 * Despite their corpse-like appearance and association with speedsters, Time Wraiths are not directly linked to the Black Flash (the Grim Reaper of the Speed Force), which does not actually punish or kill speedsters but rather comes for them when their time is up (i.e. the time of their death) to return them to the Speed Force. Rather, Time Wraiths likely work in concert with/alongside the Black Flash as each is under the charge of the Speed Force itself.
 * Its appearance bears a resemblance to the Dementors from Harry Potter, a resemblance noted by Cisco and later by Hartley.
 * Cisco Ramon called the creature "Inky", a cyan-colored ghost from Pac-Man.
 * The motives and method for attacking bears a resemblance to those of the Reaper from the Doctor Who episode "Father's Day".