FUBAR works simply, you roll a minimum of three dice, you allocate the results of the best three to different categories...
Success determines how well you've done.
Sacrifice determines what you give up in the process
Story determines who narrates what happens
High Plains FUBAR adds an automatic fourth die and a Speed category to determine who goes first when such things are important.
Dead and FUBAR'd introduces the idea of relationships, which provide instant benefits when someone bears a relationship that is significant to the action they are taking. It also brought in undead, and powers fueled by a dark hunger.
Walkabout changes a few fundamental mechanisms, but is generally the same game. It allows characters to engrave their skins with tattoos and scarification a limited number of times. Each of these symbolic skin markings is an act of honour to a spirit or an outward sign of belief and affinity to a concept. When a character performs an action aligned to that affinity, they gain a bonus.
I've thought about a system for super powers in the game, something based on narrative ideas. My thoughts worked on the idea that super powers often do amazing things, but quite often they have side effects just as dramatic as their potential benefits. Super strength may break down a barrier at the expense of innocent lives being lost in the collateral damage as the building crashes down around the impact. Mind reading may unveil secrets that completely change the nature of the story. Being invisible may cause people to inadvertently drive through you, when they think the way is clear. The paradoxes of time travel are well documented.
Taking this a step further, I've been thinking sporadically about a magic system for a while. The modifications to the rules (and subsequent new ruleset), facilitate certain things that may make magick of the "Mage: the Ascension" style more viable.
Both High Plains FUBAR and the dark powers of Dead and FUBAR'd add an extra die to the basic resolution to bring a distinctive new effect into the game. So with that in mind, maybe a dice of a distinctive colour reflecting mystical potential integrated into an action. Mage uses Quintessence as a mystical source to fuel magic, so maybe we could use a number of these dice equal to the amount of power expended. few dice, every one that is successful infuses the action with magical effect, but we still need the success to see if something superhuman occurs, and the sacrifice to see if paradox is generated.
I'm thinking that a character using coincidental magick may choose whether to include one of these distinctly coloured dice in their success/sacrifice/story allocation, while a character using vulgar magick is forced to automatically use one of these dice (the lowest one rolled...because more powerful magick is harder to control).
This needs more work, and at this stage it feels like an inelegant patch onto the core FUBAR rules, but it vaguely feels like it's heading in the right direction.
I've also been thinking of the way skills and attributes work in Mage as compared to FUBAR. Perhaps once a character has the Mage third level in an attribute or skill, they gain a FUBAR positive trait. If they have a Mage fifth level, this translates to a FUBAR double positive trait. If a character has a Mage attribute of one or a complete lack of skill in something they are attempting, this might count as a FUBAR negative trait toward the action. A character automatically applies traits from a single attribute and a single skill when they declare an action (where positive traits apply to the success and negatives apply to the sacrifice). This is different to the core notion for FUBAR magick, and closer to my storifying mage concept, but further thought down this path might bear fruit.