Entertainment Center: Genesis Level
3 items of Sega Rarity

A closer look reveals...
The Immortal, full package: Box, manual, cart, official hint book
Sword of Vermilion, full package: Box, manual, cart, official hint book
Crusader of Centy, full package: Box, manual, cart, official hint book
Though The Immortal itself, complete, is a rare enough thing, but having the actual mail-in only official hint book puts it through the roof. It was only available if you bought it through the mail-in card in the game box. The hint book is pretty cool, it's written from the wizard's, that you control, point of view. He goes all the way through the dungeon, solving the puzzles, thus helping you solve them in the game, talks to the other characters, etc. It's a very well written book.
Though upon its release, the option was given to buy the hint book(then, shrinkwrapped to the back of the box) with the game, most people felt the $10 increase in price wasn't worth it. I bought the hint book(I think it was $3), alone, from a guy a long, long time ago, just to have it in case I ever bought the game. Found the game a couple of months ago, complete, except for the hint book, for $5! Now I have it all...
Ah, the already hard to find Crusader of Centy, coupled with the extremely hard to find official hint book. The game is fucking great, even if it is a "Zelda 3 clone"! One piece of advice, though the hint book is a pretty rare thing to find, it's not worth your time. It's almost pure text, with very few maps and pics...and it's in black and white! Ugh! Amusing Note - On the inside of the first page there is a message: "Congratulations on your purchase of the best action/RPG game currently available on any system."