Joined: 06 Sep 2006
There is indeed a "hack menu" in ScummVM, and we call it the debug console. You'll enter it by pressing Ctrl-D. You'll find a small documentation there.
*Edit: I don't know what you're supposed to do to enter this mode on your DS*
Each engine, sometimes even each games, as his own set of implemented functions (if any). You'll find the list by typing 'help' in the console.
It may not be that helpful with Elvira, as I don't think there's a invulnerable mode in it... but it's worth a check anyway.