The Lights in the Sky are Stars
Game rule description: Announce that you are using the impossible skill, and give an explanation of what you’re trying to do with it; entertaining descriptions are much more likely to be granted an attempt than otherwise. If allowed, spend an action point and roll the skill check; should it succeed against the DM-set target DC, the action is performed. The DC for attempts to defy death are significantly higher than other uses of this skill; should the skill check fail for these attempts, the player remains alive and conscious for the remainder of the fight, but as soon as the fight ends, the character immediately dies.
Another way to describe it is that you are deliberately invoking the Rule of Cool. (Source also lists, if you include the sub-tropes, literally hundreds of examples to draw from for ideas.) See also: Crowning Moment of Awesome
Your skill modifier for this skill is half your level rounded down, plus either your wisdom or charisma modifier (whichever is higher), plus any bonuses you get from related feats.
Flavor description: Each class uses a power source to fuel their abilities; arcane, divine, martial, primal, or psionic. Each of these, however, is itself fueled by an even deeper power source. It’s called many different things by different people; whatever you choose to call it, it represents the exertion of one’s will over reality. The traditional power sources express this will through a framework of rules that govern what they can and can not do. Those able to tap into this deeper power source, on the other hand, are able to briefly produce dramatic, explanation defying effects. These effects are amplified by emotion; therefore, a highly impressive effect is more likely to succeed than simply breaking a rule.
Using this skill represents overriding reality with your willpower. Those that use this power often become drunk on it, becoming better at channeling it, and achieving more impressive effects. At the low end, those that use it are able to accomplish feats such as lifting objects far to heavy to actually lift, to making jury-rigged machines and equipment last far longer than they should. More advanced users have been able to produce magical effects that they do not know – even warriors, on occasion. The most powerful users of this skill can blatantly violate the laws of physics.
Attempts to defy death with this skill are more difficult, though even failed checks in these attempts will stave off death long enough to accomplish a single goal (at the DM’s discretion).
An example of a bad use of this skill versus a good use:
One of the party’s spellcasters is attempting to raise someone from the dead; however, they have been dead for longer than the spell normally allows. Simply saying ‘I use the impossible skill to bring him back anyway’ won’t work. On the other hand, something like ‘Using the energy of the ritual, I force open a door to the afterlife for us to go through and search for their soul’ would certainly allow a skill check.