After watching it again:
Mai dodging fullum assasins, I have come with a theory now. Fullum assassins are probably monsters used by the saiyans to scout, like the little green monsters Nappa and Vegeta used when they came to earth in the anime. The saiyans probably sent those fullum assassins to scout or something.
I think there are 3 sides in this movie:
The Good guys: Goku, Bulma, etc.
The Antagonists: Piccolo, Mai.
The other third party: Saiyans (Under Frieza´s orders or by themselves trying to see what happened with Kakarott?)
Maybe at the end Goku and Piccolo join forces against this "mysterious" third party? (Saiyans)