Is there any added mechanic that I don’t know about?
There are two mechanics associated with many of the new events. Using Nupert's skill when adjacent to a summonable minion will have different animations for each of them for Lilly and Felix. Courage intervention events make up the other big chunk of the new stuff, they can be accessed by completing a series of self imposed challenges in harder maps. Hover your cursor over the lock in the top right corner of the screen in any map that is at 3 cloud difficulty or higher to see your challenge progress.
Check the new "bonus gifts" section in the gallery, it lists most of the new events with simple instructions on how to find them.