Most of these are pretty overpowered... though to be honest I'm leaving out the truly overpowered ones I've thought of.
Mimicry: Ability to mimic someone else's abilities after only seeing them perform them once. Perhaps even creature abilities.
Lightning incarnate: Control, create, and transform into the element lightning. Avoid physical attacks by turning body into lightning, allowing the attacks to pass through. Can also electrocute anyone that is touching. Can travel at elevated speeds. When using this ability a loud crack of thunder follows. Can also melt steel as lightning reaches temperatures of 53,540°F whereas the surface of the sun only reaches a mere 10,340°F. Can jumpstart own heart if it enters a state of cardiac arrest. Able to listen to the electrical sound waves that traverse the air itself to analyze her surroundings and defeat illusions. Upon activation all wounds, regardless of severity, are healed. Hair will appear like yellow living lightning. Eyes will be white and radiate lightning. Entire overall body will radiate a golden aura of lightning.
Weaknesses: Insulators, like rubber. Also faraday cages/suits (at least temporarily until they melt).
Lightning Spear: Conjure a spear of lightning and hurl it at an opponent - like the Greek God Zeus.
Thunder Clap: Heats the air around the character until it explodes in a thunderclap. Can be used to avoid and neutralize non-material attacks, and stun foes.
Thunder Metallurgy: Heat and melt nearby metal and reshape it into something else.
Judgment: Destroy a target from a long distance by focusing a cluster of electricity above the target and then sending a huge and powerful bolt of lightning crashing down from the sky. A much weaker form can also be used directly from the hand.
Rage: The more you're attacked, the stronger you become.
Nullify: With a single snap of the fingers the target's powers are sealed (temporarily). Could also use the power to nullify attacks (would have to be a twitch thing were it's used at the moment of impact to avoid damage).
Phoenix Rebirth: If slain within this form they'll be reborn from the ashes like a phoenix. But each time this happens a piece of the soul is lost. The character becomes more cold and detached. It's a rather unpleasant downside despite how powerful it is.
Zi Zi Bao Zing Bang Ziggy: Warp reality in ways that are so insane that it's very difficult to fight against as everything is constantly changing in illogical ways without a pattern of any kind. Up is down, left is right. No, up is right, down is left. No, up is left, down is left. Left is up. Total madness.
Wraith blade: A transparent ghostly green sword that might be wielded by an apparition. It's able to pass through solid objects due to its non-corporeal state but it's also able to behave as if it is corporeal. One could, for instance, pass the sword through another's completely negating their attempt at parrying and cut the enemy directly with armor counting for nothing.
Wraith form: Take on the form of a spectral wraith. Transparent in this form but can turn completely invisible. Does not walk on the ground but hovers. The temperature around the apparition is lowered to the point that those around can see their breaths. Capable of various forms of telekinesis, teleportation, super speed, super strength, and possessing astral perception to see through illusions. Intangible in this spectral state, able to pass through solid objects and even living beings. Also capable of various levels of manipulating the elements of wind, fire, electricity, and water.
Weakness: While intangible and seemingly untouchable, silver is able to cut the wraith and cause severe pain. The wraith is unable to cross a line of salt; though this might be able to be countered by manipulating the wind to blow an opening in the salt.
Possession: IF the wraith passes within a living being it is able to possess it. While possessed the host has increased speed and strength.
Icy Fingers of Death: The wraith is able to reach within someone's body and simultaneously freeze and decay whatever it grabs.
Memories of Pain: Through biokinesis the wraith is able to inflict pain (physical or mental) and wounds upon an enemy that the wraith itself has suffered at any point either current or in the past.
Soul Eating: The wraith is able to eat another's soul - either partially or completely. Doing so absorbs their essence and increases the wraith's own power.
Soul Summoning: The wraith is able to summon the souls of those it has slain who will appear as wraiths and attack its enemies.
Necromantic gathering: Any nearby dead are raised as zombies to fight for the wraith.
Phantom Meld: If the wraith is slain its spirit will reassemble itself after a few hours unless the bones of its body are salted and burned.