Isn't reverse engineering a game against the terms of most any proprietary EULA? Even without a decompiler or the related, one could still make out most of the details of a game just by studying the design and game mechanics. It takes a good skill with observation, mathematics, and knowing some basic computer programming rules (such as what happens when a variable overflows - I get this in Sonic 2 in Metropolis Zone Act 3 using debug - 594 frames of falling from stopped (don't recall the exact number but it was just under 600) causes the character to go in reverse (128 pixels per frame upwards instead of downwards)).