How do I make particles appear in a circle?

To make particles appear in a rectangle area we have to set "X randomiser" and "Y randomiser" to any positive values.

How to do that particles appear in a circle (not rectangle)?

If all else fails a workaround could be to store your initial X Y coordinates, and move at random angle a random distance every frame that it makes a particle. Then again, there might be a less finicky and more optimized way to achieve the same effect.

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If I understand you correctly, you could create a sprite (use a round image). Lets call it circle.

Give the circle sprite rotate behavior.

Create an imagepoint(1) on the edge of the circle.

Put the particle object in a container of the circle sprite.

Pin the Particle object to the imagepoint(1).

Set the circle's property to invisible.

Also when you create the circle or spawn it, add "set postion to another object" and set the particle to the circle at the imagepoint(1).

Now you can spawn the circle or use system "create object" to create the circle and the particle effect will be created with it and will rotate in a circle.