at levels 4, 8, 12, & 16, a character will receive both an ability score improvement and a feat of their choice.
characters roll death saves blind, only the game master will know the result. upon death or stabilizing, all rolls will be revealed.
these options can be used once per turn, so no, they cannot be combined.
nudge fate. for 1pt of inspiration, you can tip the scales and add 1d6 to any attack roll, saving throw, or skill check. you can declare this after seeing the roll, but before you know the result.
accelerated recovery. for 1pt of inspiration, your wounds knit together much faster than most. during the short rest, you regain additional hit points equal to the number of hit dice spent × your proficiency bonus.
spin the thread. for 2pts of inspiration, you can influence fate further and reroll any attack roll, saving throw, or skill check. you can declare this after seeing the roll, but before you know the result. you may then choose any of the rolls.
preternatural assurance. for 2pts of inspiration, you hope to predict the outcome of threats. roll the saving throw as normal, on a success, you take no damage. on a failure, you take full damage. you must declare this before you roll.
defy death. for a variable amount of inspiration, you spend all your current inspiration in order to automatically stabilize. you must decide to do so when you go unconscious due to dropping to 0 hit points.
rider of the pale horse. for 3pts of inspiration, you can cheat death and auto-stabilize on all death saving throws. in the following round, you regain hit points equal to a roll of your hit dice + con mod. this can be used once per session.
shared avoidance. for a variable amount of inspiration, you are guaranteed an encounter-free night. the number of inspiration required is equal to the number of player characters resting.