Shadowboxing - S4-E9
Corrected entry: Sylar takes over Parkman's body, and has discussions with Parkman, who is a figment and isn't really there. However there are many times when a shadow is cast on Parkman. Most noticeable when they are in the diner in Texas and Sylar threatens to kill Lynette, and Parkman interjects (when Sylar instead takes a straw). You can see Sylar's shadow on Parkman, which isn't possible if he's not really there.
Correction: This is inside Sylar's imagination and in his imagination Parkman is there, thus he imagines a shadow falling over him.
lionhead