Echidna

Echidna is a powerful "Endbringer".  Her eventual intense hatred of the Undersiders directs her to focus primarily on killing the team. She is amazingly destructive, powerful, and hard to stop. She qualifies as a Class-S threat, along with Endbringers and Slaughterhouse 9 attacks. 

Powers

Echidna consumes tissue and 'evolves' body parts, varying from wolf-like heads to tentacles.  Touching her will result in clones of yourself that are stronger and 'meaner', and impossible to control (with all the powers you may have).  If she maintaines contact with the original, she can continously produce clones. Clones, along with vomit, are her only excretion; she eats only meat and it adds directly to her mass. She has also developed an extremely unstable temperment, probably as a part of or a direct result of her power. Her displacement from Earth Aleph and Simurgh 's tampering also contributes to her unstable state.

She is also (according to 17.8 of the  Migration arc) impossible to kill. While seemingly indestructeble due to her quick regeneration, she in fact can be killed. Anything cut away from the core of her body will deteriorate and die, while anything left remaining attatched to the core will quickly regenerate. If Echidna's core is destroyed, the rest of her is destroyed, as well. 

It is likely that her power was affected by the fact that Echidna was administered only half of a dose of power elixir; her unstable temperament and monstrous lower body were probably not in the intended spectrum of effects.  Oliver, who drank the second half of the dose, may have received the portion of the power intended to moderate and control these effects.

Other Information (Spoilers! Better check yourself before you wreck yourself)

Clearly you're aware of the spoiler risk. If you're just here to brush up on old news, then you're probably one cool cat. Otherwise, you're about to see many plot spoilers.

Echidna is the codename for Noelle. A PRT member suggested the name because he named Noelle and didn't want the name tainted by a monstrous parahuman.

Echidna dies durring a Class-S battle with the Protectorate and Brockton Bay villains. Sundancer incenerates her, even though several capes are still trapped inside her body. 

Echidna enters into "Rage States," where Noelle is copletely out of control while her mutated body rampages. During these rage states, Noelle is unaware of what her body is doing, instead experiencing memories. Noelle often gives her body complete comtrol in exchange for enjoyable memories. While generally gratifying, these visions can occasionally be either unpleasant or unrelated to Noelle.