Hi!

Part of my mod requires the player to be completely by himself with no help from followers in order to overcome a trial. I have looked around and didn't find a way of doing this and I can't remember a quest in Skyrim which does this as reference...

How do I go about doing this? Either via "You must dismiss your companion before continuing" or dismissing them automatically via a quest script?

Cheers!

You can look for example at the Dark Brotherhood Sanctuary in Falkreath--I don't think followers will go in there. But there isn't a 100% reliable way of doing this. Custom followers often have "summon" spells, which can circumvent most methods: the player may appear to be alone temporarily, then call in the follower when needed. You could perhaps have a trigger box covering your trial area, and move any followers who enter the box back out.