The OverTheWire Advent Security CTF had one problem this year [0] which involved reverse engineering a (self-modifying) Master Boot Record binary similar to this which implemented AES-ECB-128, felt very rewarding to complete. I made heavy use of bochs [1] which seems to be the most common tool for emulating and debugging protected mode and bootloader code such as this. The creator of the CTF challenge talked about it on twitter as well [2].