[...]
   //some initialisiation-stuff is done here
   
   define iterator, Skill1;

   // set the initial size equal to 10% of the original size
   my.scale_x = 0.1;
   my.scale_y = 0.1;
   
   // increase the sprite's size
   my.iterator = 0;
   
   while( my.iterator < 6)
   {
      my.scale_x += 0.2;
      my.scale_y += 0.2;
      my.iterator = my.iterator +1;
      wait(3);   // wait(1) looked terrible so I tried a higher value here
   }
   
   decrease the sprite's size (at a slower rate than it was increased previously)

   my.iterator = 0;
   
   while (my.iterator <= 10)
   {
      my.scale_x -= 0.1;
      my.scale_y -= 0.1;
      my.iterator += 1;
      wait(3);
   }

   wait(3);
   ent_remove(me);

   //some initialisiation-stuff is done here
   
   // set the initial size equal to 10% of the original size
   my.scale_x = my.scale_y = 0.1;
   
   // increase the sprite's size
   var c;   for(c=0; c<15; c++)      //15 is number of frames, change in all parts of loop if changing.
   {  my.scale_x = my.scale_y += (1.0)/15;
      wait(1);                               }
   my.scale_x = my.scale_y = 1;

   //decrease the sprite's size (at a slower rate than it was increased previously)
   var c;   for(c=0; c<30; c++)      //30 is number of frames, change in all parts of loop if changing.
   {  my.scale_x = my.scale_y -= (1.0)/30;
      wait(1);                               }
   my.scale_x = my.scale_y = 0.1;

   wait(3);
   ent_remove(me);