Parallax

Animation progress is tied directly to scroll position, so scrolling forward or back plays or rewinds it.

Add a "Scroll-Linked Animation" (also called a scroll-driven animation or scroll scrub) to [where].
The animation should move exactly with the scroll position, so scrolling down plays it forward and scrolling up rewinds it on the spot, with no time-based easing of its own.
Map the whole animation to a clear scroll range, and show a sensible static state for users who prefer reduced motion.

An element or scene scales up or down as the user scrolls.

Add a "Zoom on Scroll" effect (also called scroll zoom or scale on scroll) to [where].
While the section is held in view, the element should grow smoothly from a small card until it fills the whole view, in step with the scroll, and shrink back when scrolling up.
Scale it without pushing the layout around it, and show it at its final size without the zoom for users who prefer reduced motion.

A still image slowly zooms and pans across its frame.

Add a "Ken Burns Effect" (also called slow pan and zoom) to [where].
While each image is shown it should very slowly zoom and drift in one direction only, then cross-fade to the next image, which moves in a different direction: calm and continuous.
Keep every image covering its whole frame at every moment so no edge ever shows, and keep the images still for users who prefer reduced motion.

An element stays locked in place during a scroll range while other content or animation progresses.

Add a "Pinning" scroll effect (also called a pinned section or sticky section) to [where].
One panel should stay locked in place while the content beside it scrolls past, switching to match the step being read, and it should let go when the section ends.
Prefer native sticky positioning over hijacking the scroll, and make sure every step still reads well without the pinned panel on small screens.

A bar or ring fills as the user scrolls through the page or article.

Add a "Scroll Progress Indicator" (also called a reading progress bar) to [where].
A thin bar along the top should fill from left to right in step with how far the reader has scrolled, reaching full width at the end.
Tie it directly to the scroll position with no easing lag, and keep it from covering the content.

Scrolling settles onto defined snap points such as slides or sections.

Add "Scroll Snap" (also called scroll snapping or snap scrolling) to [where].
When scrolling stops, the view should settle neatly onto the nearest section so each one lines up with the edge instead of stopping halfway.
Use the browser's native snapping so wheel, touch and keyboard scrolling all keep working, and make sure content taller than the view can still be read in full.