Looking for recommendations to implement traps on stairs.

Here is what I am currently brainstorming,

I have stairs going into my next level area, I hit a trigger or pressure switch at the bottom of the stairs that starts boulders rolling down the stairs that can damage the player, they can continue to fall as the player passes them or they stop when you reach the top.

If I have the boulders hanging and the trigger causes them to fall, what would be the best way to get them to fall and roll to the bottom and restart. I wasn’t sure if I should use spline or let the random fall and roll take over.

To make this trap harder I am wanting to add some type of blurred vision from the trap and make it harder to see while going up the stairs.

Is it possible to make the trigger activate physics of the boulders?