Matching the Genesis Frogger to the arcade version was a lot of work and a long story but I really enjoyed it. Here are a few details:
I started off with an arcade emulator of Frogger downloaded from the Internet, with images of the original ROM data. I ran the ROM images through a disassembler, printed them out, and studied them, also dumped them in hex and created a hex editor, and made videotapes of myself playing this emulator.
Although the Genesis has a complete Z80 system it seemed impractical to port the arcade's Z80 code to run on the Genesis Z80 because of the specific screen mapped display functions it used.
I did, however, locate the music and graphics data in the arcade image ROMS. The graphics were converted with a utility I wrote. The music sequence data was loaded directly into the Genesis version, and I wrote a sequencer in Genesis 6800 code to play it.
The game logic was controlled by a new program I wrote in 68000 assembly language. I was able to match the action by studying the video tapes and duplicating the positions, speeds, and sequences of all the sprites. Sometimes I was able to match motions of objects and rows by carefully timing them with a stop watch. Some functions were divined by studying the disassembled Z80 code from the arcade game. The sound of the frog jumping was duplicated by recording on tape the arcade sound, slowing the tape to half speed, figuring out the musical notes, then locating the sound chip register settings that played those notes.
I only had enough skill to play the first 5 or 10 levels of Arcade Frogger so I had to invent the patterns of the higher levels.