i think you should use the RST behavior instead of the bullet one and for the chance code you can use the random command and you should also create function witch is going to tell the behavior of your A.I. and use random time interval to make them do something
like;
pick a random "creature"
if not "sleeping"
if not "eating"
every random(10000)+5000 set the private variable of it to random(3)
then
if 0 then call function "sleep"
if 1 then call function "go"
if 2 then call function "eat"
and create your function like
sleep;
wait 20 000 ms
then call the function "go"
eat;
move toward food.x.y
wait 5000 ms
than call "go"
go;
move toward random(640) random(480) "if your layer is 640,480)
something along those line ...