How do I make sprite appears and disappears on randomly spot on screen

Add an instance variable on that object, call timeAppear=1.

Everytick, Substract dt from timeAppear

If timeAppear <=0,

Trigger once:

- Set object opacity to 0

- Set position:

X random(100,layoutwidth -100)

Y random(100, layoutheight -100)

If timeAppear <-1

Trigger once:

- Set object opacity to 100

- Set timeAppear to 1