Internal Debugger

As with any other early SCI game, hold down both Shift keys and press the - key on the numpad at any point during the game. To exit this mode, press Shift and D.
Key(s)    Action
Q    Quit
B    Set Breakpoint
O    Show objects in heap
Shift + O    Show objects with address
A    Inspect ID in accumulator
C    Inspect Current Set of Objects

Press C to see all of the object within that
set. Press I to inspect the selector.
Press E to edit that selector.
I    Inspect Object/Memory - The player can

also press up/down to go up/down through
the memory by 16 bytes and left/right
to go up/down the memory by 2 bytes
F    Show Free Heap
S    Show sends
G    Change Global Variable
L    Change Local Variable
T    Change Temporary Variable
Enter    Single Step through Script
Tab    Step across Send
C    Show objects in heap
R    Show resources loaded
Shift + S    Shock stack usage
Shift + /    Show an incomplete list of shortcuts


(Source: HWM, ScummVM Wiki)
In-game Debug Actions

At any point during the game, open up the text prompt and enter ascot backdrop and go to a different room. The following actions can be entered in the text prompt:
Input    Action
TP    Teleport to a room
GET (insert object name here)    Does exactly what is says
PITCH (insert object name here)    Drop the object
ADJUST BAMBI    Room info on the menu bar (non-English versions only)

There are also some game state modifiers. However, the player has to be in the casino, then go to the room with the mirror and the bar entrance.
Input    Action
INCREASE BACKSTAGE    Increase state of the showroom
INCREASE NEWSPAPER    Increase state of the newspaper
INCREASE LAWYER (insert object name here)    Increase state of the lawyer

In addition, these controls become available in the game:
Keys    Action
Alt + W    Write to a log file
Alt + E    Change view of ego
Alt + R    Get the current room number
Alt + S    Switch between Larry and Patty
Alt + F    Internal debug appears when going to a new room
Alt + G    Test the room in slot 999
Alt + D    Internal debug
Alt + F    Internal debug appears when going to a new room
Alt + I    Allow typing during cutscenes
Alt + M    Show memory stats
Alt + X,
Alt + Z    Quit
Alt + V,
Alt + P,
Alt + C    Show layers of a room (Visual, Priority and Control respectively)

Lastly, this enables some debug info at various parts of the game.