Ah, here it is:
Just a quick bit of play that happened my last 5e session:
One of the characters has entered into the pit-fighting arena to earn a bit of money and fame, and because he's a dwarven battle-rager. Over the past few sessions, he's made a small name for himself in the amateur leagues, having won a district amateur championship tourney. He's also spent his winnings buying up minor magical enhancements to his armor, so that now it smokes on command and the eyes of his helmet glow red. Nifty effect, been fun so far, and the player is, obviously, loving this downtime sideline for his character. The character had just been invited to the pro-circuit as an opening act (ie, undercard), and the character hopes to earn a spot at the top of the card. Really, at this point, this is the WWE of pit-fighting, with characters and everything. It's been a hoot.
So, then, last session, another character tried to improve his status with one of the city Factions (this is a Sigil based game), the Fraternity of Order, but was stymied by a previous association with the Xaosects (imagine trying to get in good with the DA while having a record with some radical terrorists and you won't be far off). Some rolls were failed, so the Fraternity wasn't very friendly and set a task of bringing a notorious criminal to justice. Some more investigation, and the party heads off to apprehend a foul murderer hiding in the Hive (very bad neighborhood) with his gang.
Things go very, very, badly for the party. On them, they split up and ran all over the place, alerting the entire gang almost at once while being unable to provide support. Sigh. But, one of the things that the gang had was a pro-level pit-fighter named Maul, known for his, wait for it, use of a maul. Hey, I'm not winning awards, here. So, as soon as he was woken up by the commotion, and after hearing the barbarian character's warcry he's popularized with his pit-fighting persona ("TIME FOR HUGS!!!" -- he wears spiked armor, so...), Maul ran out and issued a challenge. Well, the barbarian failed to overcome Maul (he was already beat up by a group of thugs), and the entire party also went down with him (he was already the last one standing, did I mention they split up going four separate ways?).
Enter one of my few houserules of this game -- your character can only die if you say so. No one said so, so the second half of that comes in which is "I get to do something bad to you in exchange." So, what I did to the barbarian player was to have Maul take the barbarian's magical greataxe, which will now be used in the pit as a prop. The barbarian's player is over-the-moon about this. Sure, he's lost a nice magic item, and his character's reputation has suffered a bad blow (and also he was generally robbed by the gang), but he now has a full up WWE style nemesis. I've actually never once had a player so damn happy he lost a fight (and gear, and rep). This outcome alone has made this experimental houserule worth it's metaphorical weight in gold.
The other characters have similar bad things -- the ex-Illithid-thrall will be finding out he volunteered to become a thrall (I don't know why, but that's something the player will really chew on), the Grave cleric has become haunted, and the Warforged rogue has... met his maker.
And the amount of this planned before the game? None. Well, I had a few good city-slums maps and it was a simple matter to build up a criminal gang from stock NPCs (some bandits, some thugs, an assassin for the murder, a few scouts for lookouts, and a gladiator for the, well, gladiator). I let the players lead with ideas and used checks to determine outcomes. I did set DCs, but I have a handly, public chart for DCs for dealing with NPCs of various dispositions, and the player looking to get in with the Fraternity knew they were unfriendly (due to the outcome of a failed roll to improve relations with the Xaosects leading to a bender and a vague recollection that something went very badly wrong), so he knew going in it would be a uphill battle.
So, for me, I've tried to use say yes or roll the dice a bit (it's still 5e, so it will fight you if you go too far with this) for the player's downtime* goals. I'm also using fail-forward techniques to generate new circumstances. Another example for this was the barbarian's attempt to find out more about his out-of-the-ring nemesis, the man(?) who had his clan and his mentor slaughtered. I introduced a complication in a previous mission (the party recovers things as a means of making money) as being caused by his nemesis, so he was looking for him. Three checks were made, two failed, so I introduced that the nemesis was no longer in Sigil, that people were scared of crossing him, and that the nemesis was looking for information about an artifact that the party was also tracking. None of this was anything the player really wanted to hear, but it was useful information nonetheless.
/ramble
*I'm using a downtime phase of 1 game week with a few very broad activities that I have some general rules for adjudication, in this case the player attempted to Improve Relations with a faction, which is set of three checks depending on what's being specifically attempted. There's results for failing none, one, or two or more checks (essentially, you get everything you wanted, you get some of what you wanted but at a cost, and things don't go your way and you've made it worse). I'm trying sets of three checks for things to generate a more granular outcome than a single pass/fail check.