These characters may appear to have small effects on the overall plot, but things can easily change.
Charlie Maul Charlie mysteriously appeared in the first episode of the series, before dying and turning into a pie crust, or a flower, or something. But later on, it is realised how he got there in the first place, and surprises all the viewers to hear that it wasn't just a plot hole.
See him in episodes: 1960, 1965, 1966
The Emperor Another character that mysteriously arrives in the series, though darkness clouds his story.
See him in episodes: 1965, 1966, 1967
Aleks Aleks is more than just a fellow Norweigan to Jostein, he's also his brother. But will Aleks and Jostein ever see each other again? Only time can tell.
See him in episodes: 1965, 1966
Watermelon Watermelon takes over the role of Paul, as his higher knowledge causes weird collision of weird impossible things that give it the chance to be pivotal, but being the fruit it is, can it overcome this?
See it in episodes: 1964, 1965, 1966
Darth Quokka He plays a very small role in the series, but he's bound to bring laughs with him.
See him in episodes: 1965, 1966
Billy The Lion Resembling Salesman Billy likes to sell things, however, he looks somewhat like a lion, can he overcome this to get his sales, and will he actually be an important character? Probably not, no.
See him in episodes: 1964
The Others Some do simply not exist yet, others cannot not even be mentioned without ruining the plot. However one of these characters will almost be too big for the plot, as he has the chance to change the future of the Costanza Falcon's crew forever.