How do I guide the AI with a list of possible responses to choose at random?

I'm trying to get more variety from my AI, and I use several models, but they all clearly have preferred preferences for response generation. I want to guide the AI to a list of possibilities at certain points, then it pick from the list.

Say I'm doing a story with the AI and there's a village under attack by enemies. And I leave it open for the AI to fill in who the enemies are. It might pick goblins 50% of the time, then bandits another 40%. I want a bit more variety than that, without explicitly telling it what the enemies are, each time, or typing "be creative and random in your responses".

Obviously, I put in the prompt, character card, or intro that "enemies in this world are (in no order): harpies, centaurs, lizardfolk, skeletons". But this leads to it only using harpies, because its listed first, maybe a centaur in 1/5th of generations.

So then, I moved on to making a world book.
I created multiple trigger word entries for the word: enemies.
Each with a 25% trigger chance
Enemies = its harpies
Enemies = its centaurs
Enemies = its lizardfolk
Enemies = its skeletons
And this kinda sorts worked, but I think it got weird if 2 or more of the 25% chances triggered at once or none of the 25% chances were rolled.

Is there a better way of doing this? Does sillytavern have tools for this? Its a big tool, and I don't know everything its capable of.

Apologies if someone else made a thread for this, I couldn't figure out how to simply describe this to search.