I have always used the Hero System for my X-Men game, starting with 4th edition in 1991, changing to 5th edition in 2002, and changing to 6th edition in 2012. In my opinion, the Hero System is the best superhero role-playing game system: its powerful and versatile rules for character design and customisation have always made the best option for my game. At the same time, I have thought for many years that the Hero System's combat system is outdated and unsophisticated. With each new edition, I check that it's still possible to run behind your opponent on your go and attack then at half DCV, then have your opponent run behind you on their go and attack you at half DCV. Enormous energy seems to be spent by the designers on the character design rules, while the combat system continues to reflect rules that were becoming out of date in the 1980s. 6th Edition hasn't fixed this either.
As a consequence, I have had extensive house rules for my X-Men game for over 10 years. As with any house rules, they are part of how I modify the standard game system to match how I think things happen in the game world. They are also part of how I address what I consider undesirable consequences of the standard game system that adversely affect the game experience - things that slow down gameplay or make gameplay less fun, such as a core dice mechanic that involves subtraction and a Speed table that means some players get more spotlight time in combat because they have more actions than other players.
This rules supplement is composed not only of my own rules modifications but also of material drawn from or inspired by a number of sources, including: