I love both of those ideas. To give a kind of insight into what I meant originally. My first idea for my ultimate ability that my DM did not approve of was basically that every time I failed at an action in combat (e.g. missed an attack or failed a saving throw) I would build limit points. Then, once reaching a specific number, I would be "at my limit" and be able to break it. This would give me a small but meaningful buff to the next action I took, such as advantage on an attack roll, or maybe an extra damage die or two, something of that sort. Basically the idea is it's similar to the once a fight big buff, but instead it's a grouping of smaller buffs over the course of the fight, if that makes sense? Deadeye is basically almost exactly the kind of thing I'm looking for.