Evil Flippy is the homicidal side of Flippy. When Flippy's evil side takes over, he will believe he is still in the war and will murder almost everyone. He is recognized by his green pupils and sharp teeth. This will occur when Flippy is reminded of the war in some way, such as hearing gunshot like sounds.
In Double Whammy he appears as a separate entity and he fights Good Flippy (normal Flippy) in this episode. In the end it was revealed that this separate evil side didn't exist and was just Flippy attacking himself, meaning that Flippy was seeing a hallucination of his evil side. In reality, Evil Flippy is a part of good Flippy's mind and they are the same person.
Evil Flippy is best known for being a killer. He is ruthless and does not seem to think or have any conscious thought other than trying to harm others. In rare instances he will display other emotions, however these instances are very uncommon.