If I understand you
you have 20 (invisible?) sprites that you are going to use to spawn an enemy sprite from.
the enemy sprite should appear, pause for a few seconds and then disappear
if so look at
every x seconds
system : pick random instance "InvisibleSprite" -- "InvisibleSprite" spawn another object "EnemySprite"
give the enemy sprites the fade behaviour set to something like :
fade in 1 sec
pause 4 seconds
fade out 1 sec
fade to destroy
(and if that was a clear as mud....
https://www.dropbox.com/s/sbqcstx64kmza ... point.capx