When the PC first arrives at the mesa top, Denom and the Ciphers at the Mesa top will be battling a group of weedlings in one of the greenhouses. If the PC chooses to help out, he'll get an xp bonus. If he just stands by, the Ciphers are eventually victorious, and the PC gets no xp.
Character type completion breakdown
Combat Boy - Helps kill the weedlings.
I helped the Ciphers destroy the weedling infestation.