Negative Speed Force

"Breathe. You're reaching out and nobody's there. The loneliness is pain. Pain racing through your mind. Crushing you, wrecking you, shattering your soul into a million little pieces. And suddenly, you are no longer you. You're part of something different now. Part of a negative force."

- Eobard Thawne to Nora West-Allen

The Negative Speed Force is an artificial extra-dimensional energy source that was created by Eobard Thawne after he had replicated The Flash's powers.

Overview
The Negative Speed Force is an artificial extra-dimensional energy source that was created and used by the Reverse-Flash. Speedsters who have a Speed Force connection can gain a connection to the Negative Speed Force by using negative emotions such as hate, fear and anguish to the point where it corrupts them from the inside and will fuel their powers.

When using the Negative Speed Force, a speedster's natural yellow lightning and eyes will turn fully or partially red, and they will harness Negative Tachyons through siphoning them from the Speed Force to accelerate their own movement. This production of tachyons means that it's users can be tracked more easily.

Original Multiverse
At some point, Eobard Thawne created his own variation of the Speed Force, which he called the "Negative Speed Force", which is fuelled by negative energy and emotions to both prove his superiority as the Reverse-Flash and to travel through time without alerting The Flash to his presence.

In 2049, Eobard taught Nora West-Allen how to use the Negative Speed Force to travel back to the present without alerting her father to her presence.

Eobard later revealed to Nora and Barry that it was part of his plan to allow Nora to connect with the Negative Speed Force as once Cicada's Dagger was destroyed she would be erased from the timeline. Nora eventually decided against going into the Negative Speed Force due to it making her more like Eobard, and she was erased from existence.

New Multiverse
After the Crisis, Eobard Thawne's consciousness was transferred into Nash Wells' mind. Eobard connected to the Negative Speed Force in an attempt to stop Cisco Ramon and Cecile Horton from exorcising him from Nash's mind, but Cisco managed to place power dampening cuffs on Nash's wrists just in time. Thawne promised that they wouldn't be able to hold him when he gained full control of Nash's body, but he was eventually removed from his brain which resulted in him being trapped as negative tachyons.

Users

 * Reverse-Flash (Eobard Thawne) (creator)
 * XS (Nora West-Allen) (formerly; erased from existence)

Powers
Most powers granted by the Negative Speed Force and the same as those granted by the regular Speed Force with a few exceptions:
 * Reconnection: If a user of the Negative Speed Force loses their connection, then they can regain it by feeding on the negative emotions of others.
 * Temporal Bunker: The Negative Speed Force exists outside the timeline and so its users can avoid being erased from existence due to timeline changes by running and staying inside of it.
 * Undetectability: Users of the Negative Speed Force are undetectable by normal means by the users of the Speed Force.

Weaknesses
Most of the weaknesses of the Negative Speed Force are the same as those that exist for users of the regular Speed Force with a few exceptions:
 * Gravity: A speedster will lack the weight necessary to access their powers while exposed to irregular gravity.
 * Negative Tachyon Production: Users of the Negative Speed Force produce a massive amount of negative tachyons while running which can easily be tracked.

Red
The lightning of most users of the Negative Speed Force will be red due to it being a physical manifestation of negative emotions as seen when Eobard Thawne uses his powers.

Red and Purple
Nora West-Allen's lightning was red and purple when she managed to run into the Negative Speed Force to return to the present day.

Trivia

 * Eobard Thawne claimed that the Negative Speed Force is the only location that is immune to timeline changes. However, this is incorrect as both the Temporal Zone and the Speed Force have also been shown to be immune to timeline changes.
 * The Negative Speed Force is not dependent on the existence of the Speed Force as shown by Thawne still having access to his powers when possessing Nash Wells after the death of the Speed Force.