Hi,
It sure has been awhile since I posted my last Scooby Doo, trick.
If doing a packet trick, I feel justification is important.
Scooby Doo spells with 9 cards or there are nine batters in a baseball line up for example.

You must remember the bottom cards so you can easily mix face down with an OH mix and milk your key card on bottom 
You have them pick a card in the middle and place it on top
Have them roll an imaginary die and you then show a list with a numbers 1-6 and monster next to it. 
Have them think of monster next to the number
You can choose six from below:
https://scoobydoo.fandom.com/wiki/List_o......villains

You have them deal number of cards 1 by 1 equal to the thought of number next to their chosen monster and drop packet on top  
You have them deal the same number plus one more to try to confuse you and drop packet on top again.
Say, "You could have picked a low number like 2 or high number like 5" and you will pick up the packet then deal 2 then 5 and drop on top 

Have them deal again the chosen number to "lock it in "
You then Deal cards in a row face up, gather up, turn face down and do a false cut.
 
The monster will be 2nd from top! But what about your key card that started at the bottom? If key card is on top, magic number =4.
If in the 3rd position, the thought of number is 1.
If in the 4th position, the number is 2.
If in the 5th position, the number is 3.
If in the 6th position, the number is 5.
If in the 7th position, the number is 6.
Note- If you fan cards towards yourself, bottom six ( cards 4-9 from top) exposing the card 3rd from top you can also determine the number thought of.
If you do not see it, the person must have thought of the monster next to number 4.

So, after the 2nd position you then count next card in other hand as 2 then 3 then 5 then 6.
Suppose they picked number 5 who is the witch doctor on your list. 
At this point, I would remove the top card and then say, you are thinking of the witch doctor right?
I would then say , "As you know the villain normally wears a costume so we will have to shake it off! "
After removing the top card, get a pinkie break under the 1st face down and place the top card face up on top.  
Do a twirl change to prove you found the card.
You could do this with cards face down if you mark the key card.