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Next time I run D&D, I'm excited to try Judd Karlman's Bingo Style XP system because it includes a mix of classic/GM-defined goals (e.g. "overcame a challenge with cunning") to player-defined goals (with some guidance on guiding players to develop those, e.g. "Used the wisdom of my comrade’s people, taking a tale they told of their people and applying it").
Original post: Bingo Style Experience Points
Follow-up post mentioning combat/roleplay/exploration balance: Bingo Style Experience Points after a few months of leveling up
However, currently running Frostmaiden 5e in play-by-post, which has some sandboxy elements, so I tried something a bit more defined than milestones, more akin to a video game quest log...
To Level Up to 4th: Complete 4 quests in the Ten-Towns. You may replace (up to 2) Ten-Towns quests with significantly progressing or resolving your individual character quests.
Original post: Bingo Style Experience Points
Follow-up post mentioning combat/roleplay/exploration balance: Bingo Style Experience Points after a few months of leveling up
However, currently running Frostmaiden 5e in play-by-post, which has some sandboxy elements, so I tried something a bit more defined than milestones, more akin to a video game quest log...
To Level Up to 4th: Complete 4 quests in the Ten-Towns. You may replace (up to 2) Ten-Towns quests with significantly progressing or resolving your individual character quests.