Achievements and what I'm calling "Legends".
Idea for that one came while I was playing Peak. Got all achievements, then I finished all the difficultlies of the game but there wasn't an achievement for that, I'm assuming because the devs thought it might've been too hard, so I thought maybe have a higher tier achievement category would make sense, without robbing players of "I got all achievements".
Achievements: many, obtainable.
Legends: few, challenging to obtain.
Would probably be neat to attach rewards for these achievements/legends, with unlockable profile pictures, banners, frames maybe, background images, etc, to give these things value aside from ego (though they can be used by users, considering this is nostr, but it wouldn't be visible as an easily selectable option to switch to, so theres that at least).