action mainplayer() // this is the action you're calling the function from
{
   // your code
   attackit(); // call the function out of the while loop
   while (player != null)
   {
      // your code
      wait(1);
   }
}

function attackit
{   
   proc_kill(4); // makes sure that only one instance of this function running so proc_status isn't needed here ^^
   ani_attack1_speed = 8;	
   ani_attack2_speed = 8;
   while(player != null)
   {		
      randomize();   	
      my.attack_choose = int(random(2));   	
      if(mouse_left && my.attack_choose == 0)   	
      {      		
         while (ani_attack1 < 100) // Solange ani....      		
         {       			
            ani_attack1 += (ani_attack_speed * time_step)%100; // Ani Speed        	
            ent_animate(my, "attack", ani_attack1, 0); // Ani Bfehl         		
            wait(1);       		
         }   	
         ani_attack1 = 0;  	
       }    	 
       if(mouse_left && my.attack_choose == 1)   	
       {      		
          while (ani_attack2 < 100) // Solange ani....      	
	  {          			
             ani_attack2 += (ani_attack2_speed * time_step)%100; // Ani Speed  
      	     ent_animate(my, "attack2", ani_attack2, 0); // Ani Bfehl     
             wait(1);      		
          }  	
          ani_attack2 = 0;   	
        }
   wait(1);
   }
}