Interesting! I’d never considered ghosts jumping across objects, but it could definitely work! Players have to revisit areas often enough that something like an event where ghosts you previously encountered start jumping to other objects could be cool.
I completely agree, and considering Pokemon’s approach is a big part of how I arrived at my solution. Just like stepping into the grass in Pokemon, I want the player to feel like every battle they start is due to their actions, whether that’s because they didn’t see the hidden ghost and got ambushed or triggered the battle on purpose to progress.