Quoted from GravitaR:

B=Both at same time
L=Left Flipper
R=Right Flipper
#=number of presses (Just a letter then press once)

Quoted from chuckwurt:

Both flippers start every code. Then you hit the left flipper to put in your first letter (where it’s at in the alphabet. A=1,B=2, and so on). Then when you reach the letter you want, press right flipper to confirm that letter. Then put in your next letter with the left button, confirm with right.
Once you’ve put in your third letter, press the right flipper twice to end the code.
This is the process for every flipper code.

Quoted from SheriffBarclay:

Both flippers
Left
Left
Left
Left
Right
Left
Left
Left
Left
Left
Right
Left
Right
Right

Quoted from cabal:

i found this codes for the Munster Pinball, some are double finds posted by other users
I will post them in this way, like it was descripted in the Code update readme file:
- Added Team Credits ESaster egg: 1 2 3. To see it you Hold in Both flippers,
then you enter numbers with the left flipper and enter on with the right.
Finally, when you are done you have to enter one last time with the right
flipper. So 1 2 3 would be B LR LLR LLLR R
1 2 3 = Credits
4 5 1 = Dead Flip
3 3 3 = Hello World
3 6 5 = Chris Franchi
4 4 6 = Pinball Team
7 1 4 = XAQ i missed you
8 4 7 = Serial Number?
i am searching any information about the secret mania mode, this way i stumbled upon the codes.