Badsmella is Smogmella under the control of a Wicked Yo-kai. In Yo-kai Watch 2: Psychic Specters, Badsmella evolves from Smogmella when fused with Wicked Parts.
Badsmella is basically the same as Smogmella. However, Badsmella is darker, and her eyes glow malevolent red circles behind a purple mask of mist.
Yo-kai Watch 2: Psychic Specters
When Nate/Katie is in the past to help complete the Yo-kai Watch Model Zero, Badsmella first appeared when the player went to get the Watch part located in the Ironworks, inspiriting the workers to be lazy by using the black haze she had created. She then played a game of hide-and-seek with the player, and after being cornered 3 times (with two times being innocent Yo-kai hiding in the factory), Badsmella fights the player, but is defeated, and was turned into a regular Smogmella.
You can befriend Badsmella by fusing Smogmella with an Essence of Evil.