Selecting a random actor on screen

I have an 8x8 grid like pattern of actors on screen. I would like to select 3 of them at random every 5 seconds to change their animation. Whats the best way to do this? Would it be using a list or something else? Im having trouble selecting them at random.. Thanks in advance, you guys are always helpful!

Are there always 64?

If so you could:
Create a number attribute ActorNumber
Create a number attribute ToBeChanged
Do every five seconds:
Loop three times:
Set ActorNumber to 0
Select a random number ToBeChanged between 0 and 63.
Run through the actors using:
For each actor of type.
If ActorNumber=ToBe Changed
Change Animation for Actor of type
Increase ActorNumber by 1

The risk is that you change the same actor in one run, but it´s a 1:64 chance of it.

thats an interesting way to look at it, ill give it a shot. I wonder if I could also set the ToBeChanged attribute into another attribute and say that if ToBeChanged = UsedNuber it should generate a new number to  try and avoid interactin witht eh same actor. Thankyou for the advice anyway! Helps a lot!

Okay so Im having a small issue:

Because the event is on a scene when I say "switch animation to 'x' for '...' I do not have an option that allows me to change the animation of the actor currently being checked in the loop. Only 'last created', 'choose actor' or 'actor attribute'.

Is there a way to fix this that Im just stupidly missing?

I would do it with lists

Created
   Set actorlist to create new list
   Set randomlist to create new list

do every 5 seconds
   empty actorlist
   empty randomlist
   for each actor on screen
      add (actor on screen) to list
   do until number of items in randomlist = 3
      set randomnumber to random number between 0 and number of items in actorlist - 1
      if not randomlist contains randomnumber
         add randomnumber to randomlist
   for each actor on screen
      if actor on screen = get item # (get item # 0 from randomlist) from actorlist
         switch animation to xxx for actor on screen
      otherwise if actor on screen = get item # (get item # 1 from randomlist) from actorlist
         switch animation to xxx for actor on screen
      otherwise if actor on screen = get item # (get item # 2 from randomlist) from actorlist
         switch animation to xxx for actor on screen

"Because the event is on a scene when I say "switch animation to 'x' for '...' I do not have an option that allows me to change the animation of the actor currently being checked in the loop. Only 'last created', 'choose actor' or 'actor attribute'."

You drag the "actor of type" label from the loop header down to the animation block. :-)
This refers to the current actor of the loop.