A Simple Solution to Unspent XP

TL/DR: Luck = Re-roll a skill check. Once per session (or whenever players can spend XP).

Pondering on the best forms of advancement, I've come to the conclusion that an open store of character abilities and upgrades, that cost varying degrees of XP, is the best way to go. If you keep the numbers small, purchases are simple. If you keep short and interesting prerequisite trees, progression feels good. But, I'm faced with examples of games that have a weird problem: when some players want to save up to buy the good stuff, they are under powered until they do so.

This creates unwieldy swings in character balance. Some games can handle different characters taking front stage, but in a combat-focused game like Hostargo, I'd like everyone on the same page at all times. This creates more of a team focus and less of a rotating rock-star spotlight. Anyone who's played a serious game of Shadowrun knows the frustration of being just 1-2 karma short, and not getting anything fun to show off for the next session.

Monte Cook's Cypher system gives us a solution, and a poor implementation. In the game, you can spend hard-earned XP on skill check re-rolls, allowing for heroic moments where you just really need your character to succeed. The problem? That XP is gone forever. NOPE!

I've been told there's an "optional rule" for keeping XP for advancement even if you've spent it on re-rolls. YES! I'm calling this spending XP as luck. It should absolutely be the default, and it is the simple solution we're looking for. Characters who keep XP from session to session will have a little extra boost when they need it, compared to their comrades who are pulling out their new and shiny stunts. This keeps any character relative to their party, even when they haven't actually "advanced".

As bonus points, XP should be able to be spent as soon as it's earned. This makes for a quick-and-dirty, yet meaningful reward cycle. As characters succeed in story-based objectives, they get a small boost to help them further down the line. Once a session is over, or characters have the opportunity to spend XP (i.e. during a long rest), XP that has been used as luck can be either spent on advancement, or saved to be used again as luck on the character's next bout.