Just a small community opinion. Comment down the name of your worst unit, say why it's bad and say how it could be improved.
I'll kick of the list by saying the Rainmaker family. Her tentacles die easily and her trait (water) barely contributes to anything, unlike Brain Freeze of the survivor side, where his trait actually does something.
I feel she could be improved by
A. Having the same slow-down effect as Brain Freeze
B. Increase tentacle health
C. Increase range.