X'iv recieved her Super-Skrull training on Tarnax VII alongside Xavin and under Chrell, "many months" before the Secret Invasion event.
The character was created by writer Chris Yost and artist Takeshi Miyazawa.
X'iv participated in the Skrull attack on New York under Commander Chrell, who seemed to be keeping her as an ace in the hole. Chrell decided she was "needed after all" when Hulkling (or "Dorrek VIII" to the Skrulls) provided difficult to kill, and sent her to eliminate Hulkling and any Skrull that saw him. Though Hulkling and his protectors (Xavin, Wiccan and Speed) escaped from X'iv, she recognized Xavin's heartbeat and relayed this information to Chrell, thus inspiring him to scan for Majesdane energy signatures and capture the other Runaways (flanked by other Super Skrulls, including X'iv herself).
X'iv then located, ambushed, and captured Hulkling and co. before teleporting them to Chrell and the rest of the Runaways (the unnamed Super Skrulls having apparently left to do invasion things). The ensuing brawl saw X'iv smack around a lot of the heroes before being subdued by Hulkling, who caused X'iv to hesitate by attacking her faith (presumably lent weight by his semi-mythical status) before knocking her unconscious with a headbutt.
X'iv's fate after Chrell is defeated is left up in the air. Given the obscurity of the character and even the crossover itself, it's not likely to descend any time soon.
X'iv's abilities are similar to those of Cloak, Dagger, Daredevil and Elektra, though a number of subtle differences in their manifestation suggest that her Super Skrull modifications simulate rather than truly emulate these abilities. Despite training at the same time as Xavin, she can use all of her powers simultaneously.
X'iv boasts a hooded cloak similar to that of Cloak's, and is likewise capable of levitation and teleporting at least a few miles at a time. It is unknown if she can open an actual portal to the Darkforce dimension, and unlike Cloak her body is visible within the cloak. Interestingly, she capable of conjuring what appear to be black energy blasts, which Cloak cannot.
X'iv can conjure energy "knives" like Dagger (though she appears to prefer formless energy blasts) that appear to behave similarly to Dagger's "life force" draining capabilities. Unlike Dagger, she can blast this power from her eyes like Cyclops.
X'iv possesses Daredevil's heightened hearing and is capable of "seeing" the world with sonar and identifying Xavin by heartbeat, as well as picking out his voice out of an entire panicked metropolis (while the heroes were in the sewers, no less). She also uses a copy of Daredevil's extending billy club. It is not shown whether she possesses his other senses or extreme agility.
When using her extreme hearing to scan the city, X'iv's eyes are a pure white, but appear normal when she attacks the group in the in the sewers (and she uses her hearing to defeat Xavin's invisibility and identify his heartbeat). It's unknown whether this is a continuity error, or if surveying the entirety of New York required her to blank her eyes for some reason.
X'iv possesses Elektra's combat ability and, apparently, prefers throwing sais to energy blasts unless surrounded (possibly because these energy blasts don't seem to hurt very much). Oddly, she doesn't seem to possess Elektra's psychic abilities, which implies one quarter of her Super Skrull abilities is nothing more than martial arts training. She also wears a version of Elektra's costume under her cloak, though it is unknown if this confers any sort of advantage.
Intriguingly, X'iv never uses her Skrull shapeshifting abilities. Though it may simply have never been tactically advantageous to do so, it's possible her Super Skrull abilities somehow impede her shapeshifting (such as being unable to change the appearance of her cloak or costume).