evil twin
noun
°A duplicate or counterpart of something or someone that acts in a contrary, nefarious, or insidious manner.
"As a ploy to discredit the reformist politician, the opposing party had hired a lookalike to act as his evil twin and be seen in a variety of compromising situations."
°A rogue wireless access point installed near a legitimate one for purposes of eavesdropping or phishing.
synonyms: alter ego, changeling, doppelganger