Warning: this slide might be a little off balance.

What you're trying to achieve here is quite difficult to do solely with Storyline. Your trigger to update a variable when “Oval1” enters the slide won’t work because the object is already on the slide from the start. You could only change the variable’s value if the object enters the slide from outside the visible area (e.g., from off-slide left or right using motion path).

Even then, you’d need to precisely time when that action should occur, specifically when the object actually scrolls into view as the scroll panel moves. Unfortunately, triggers like "Object intersects start/end" won’t work reliably in this context due to various limitations.

In one of my previously attached examples, I included a simplified version using no JavaScript. However, the animation and detection behavior you’re trying to achieve does require JavaScript (also attached earlier in this thread). I've now attached an updated version of your file with a simple JavaScript snippet that accomplishes what you need.

The code is reusable, you can apply it to another slide or duplicate it within the same slide, as long as you change the marker object ID (e.g., "Oval1") and the variable name in the code accordingly.

By moving the marker object up or down relative to the object you want to show or hide based on the variable change, you're effectively adjusting the timing of when that object appears or disappears.

Btw, I really like how your slide looks with the “extended slide” tweak.