Here is the current design of Plascy!! Her cutie mark is an eye behind a curtain. Character description:

Plascy is a unicorn and an evil mastermind hidden in plain sight. While mostly untrustworthy, her façade of a bubbly personality makes her generally likable, even by ponies that aren't necessarily attracted to larger ponies. She is a good friend and nopony will suspect her intentions of breaking friendships at the first sign of disloyalty, distrust, and a lack of common interests before it's too late. ||An alternative backstory is that she's a Federal agent.||