The Last Guardian (Atari 8-bit family)

No relation to the PS4 game, The Last Guardian is a rather difficult shmup.

Hidden Message#

Hidden on the disk starting at sectors 190-192 is the following message:

HI THERE HACKERS, CHRIS HERE. I'VE LEFT IN THE CHEAT MODE I USED 
TO TEST THIS GAME AS I MADE IT - SEE IF YOU CAN FIND IT.......?
BY THE WAY, MEGADETH, METALLICA AND SLAYER ARE FRIGGING MAGIC! 
GARFIELD ROOLS O.K. AND JACK DANIELS (Hic!) BURP! IS *THE* DRINK.
GO AND BUY MY HENRY'S HOUSE AND MIRAX FORCE AND WATCH OUT FOR MY 
NEXT TWO GAMES:SPOOKIES+ACILLATEM. FOR NEXT SEC, USE MASK $40.

As indicated by the message, the next sector (193) contains hidden text that can be revealed by XOR-ing its bytes with the value 40:

YOU CAN CONTACT ME AT; NORTHESK HOUSE, KINNABER ROAD, MONTROSE, 
SCOTLAND DD10 9EP. A SPECIAL HI TO TINA MISS MUCK xxx BYE CHRIS.

The cheat mode is enabled by entering 18.8.67 with the keyboard on the title screen. This turns on invincibility, and is indicated by the message "cheat mode:operational" displayed at the top of the screen during gameplay.