Lightning dagger

The lightning dagger was a piece of meta-tech and the primary weapon used by Orlin Dwyer in his rampage as Cicada. It was owned by a future version of Grace Gibbons, after she took on her uncle's mantle as Cicada; the lightning dagger was destroyed by Barry Allen.

History
When the S.T.A.R. Labs satellite was knocked out of orbit by Clifford DeVoe following the failed Enlightenment, pieces of the satellite (which DeVoe had loaded with dark matter) impacted in 46 different locations. Cicada's dagger was a piece of shrapnel from the core of the satellite, where the dark matter concentration was the highest.

The dagger is the same piece of shrapnel that gave Orlin Dwyer the wound in his chest. As a result, he became connected to the weapon, due to the fact that he obtained his powers alongside it. The dagger has become Orlin's signature weapon to kill meta-humans in his mission as Cicada.

After Team Flash used their meta-human cure on Orlin, his bond with the dagger was severed. However, at some point after she awoke from her coma, Grace took on the mantle of Cicada to continue her uncle's legacy after he was cured. Eventually, Grace traveled back to March 2019 to S.T.A.R. Labs (the time and place Orlin was given the cure) to rescue her uncle after he took the cure, though she was too late. A battle between her and Team Flash ensued, taking them all out, she killed Dr. Ambres with Orlin's dagger (which Grace herself seemed to have bonded with) and took an unconscious Orlin to a cabin in the woods to be healed.

Ralph couldn't figure out why Eobard Thawne was so keen to help Nora to stop Cicada, insisting that they'd have to destroy the dagger in order to defeat the serial killer, since Cicada II didn't have the dagger in the future (in which Team Flash never managed to defeat her) Ralph then realized that the dagger is Eobard's plan.

Erased future
In 2049, the dagger is strapped to Eobard's chest, dampening his powers while he sits on death row in Iron Heights Prison.

Powers

 * Psionic bond: The dagger shares a psychic connection to Orlin Dwyer (and later Grace Gibbons ), as it originated from the same satellite which gave him his powers. Orlin can mentally summon the dagger to him from any distance and is the only individual who can use it. In the future that an older version of Grace comes from, she too gains a connection to this dagger, being able to summon it back to her from great distances.
 * Power negation: The dagger has the ability to negate meta-human powers within its presence.
 * Electricity generation: Cicada's dagger can also generate red electricity.
 * Force-field generation: When the dagger lodges itself into the ground, it generates a force-field of red energy.
 * Meta-human detection: The dagger glows red if a meta-human who gained powers due to exposure to dark matter is near.

Weaknesses

 * Larger quantities of dark matter: Team Flash were able to temporarily negate the influence of the dagger by imbuing a piece of metal with a higher concentration of dark matter energy.
 * Non-dark matter-based powers: The dagger is only able to negate the powers of meta-humans specifically created by exposure to dark matter. Caitlin Snow's Killer Frost powers can still manifest in the dagger's presence, since she gained her powers through other means.
 * Mirror gun: After being tested by Cisco on the satellite core from which the dagger originated, successfully obliterating said core, the team concludes this weapon can in fact destroy the dagger.

The Flash
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Season 5
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Trivia

 * The dagger glows when a dark matter-empowered meta-human is nearby, similar to the way that elvish blades, such as Glamdring, Orcrist, and Sting glow when orcs or goblins are near in The Lord of the Rings.