Outline

Add an outline on all objects of the layer having the effect. This won't work well if shown on top of the background color of the scene. Be sure to use an object acting as a background or a floor.

The outline traces the shape of the non-transparent pixels, and you can choose its color and thickness. Applied to a single object instead of a layer, it's a common way to highlight an item the player can pick up or select — for example, switching the outline on when the object is hovered or reachable, and off otherwise. This is a 2D-only effect.

Reference

All effects are listed in the effects reference page.