The Sinister Six? More like Sausage Fest Six.
Scorpia aka Elaine Coll
Powers/Weapons: Her scorpion suit which give her enhanced speed and strength. The tail and pincers can fire electricity, lasers, microwaves, or plasma. Also pincers for stabbing.
Backstory: A mental patient of Hell's Kitchen, she was recruited and outfitted by super villain organization Maggia, specifically Silvermane. Betrayed by her employers she eventually joined the new Sinister Six/Seven and continues to sow chaos. Her life prior to the mental ward has yet to be explored save that she was committed for torturing and killing two police officers while singing.
Reason She'd Be An Awesome On-Screen Baddie: She's insane. Not quite Heath Ledger Joker levels but a Chaotic Evil character always shakes things up. Plus she has all those wonderful toys just begging for a vfx eyegasm action sequence, preferably involving parkour and witty barbs.