Hello, what I do when I whant to make "random" things and give to my missions a semi-dinamic appearance is to create a dynamic group, for example, with a whale, shrimp, fishing boat and a sailboat; everyone with 25% and only one can appear.
Then I make triggers for any possibilitie.
I made a SC campaign (unfinished

) in which maybe India, Join Russia in a war, or maybe join USA, or maybe remains neutral... so I made 3 possibilities (40% Russia -whale- 30% USA -sailboat- 30%neutral -fishing boat)
And then 3 destination goals with the 3 possiblibities, "if whale...."
Maybe is a long and "manufactured" way to do the things and maybe there are easiest ways of making this (I´m not too used to the DW editor), but that´s what I did.
Hope This can help you and everybody and sorry if you don´t understand something, I´m from Spain and improving my English