Batty is an old computer game, a descendant of the popular Arkanoid. I ran across it with it while I was playing games on the Spectrum and I liked it so much that I decided to write a remake on the PC, together with a friend.
We've completely redrawn the graphics (pixel by pixel in paint) and doubled the resolution. The engine is written from scratch and it mimics the original with high fidelity, although we did not make use of disassembly and only wrote it based on the observed behavior of the game.
The game works entirely in text-mode, though if you didn't know you probably couldn't tell. We used a bunch of tricks of the VGA card and unfortunately one of the intro screens has a bug because my video card (an S3) worked differently than most others.
The game redefines that text characters to produce the graphics. You can still test it under Windows in full screen, and it works nicely in dosbox (even with sound) except for a colorful logo that was based on the video horizontal retrace.
The game was written in assembler, initially wrapped in a Borland Pascal file because of the (at that time) nice IDE, but later on we moved it to plain assembler. We also use our own packer so in the end the size including all graphics is only about 25k.