In my last session where I am GM, an accident happened. My player attacked unwillfuly an NPC who wants to punish them for that. As they are actually my best player, I really don't want ruin their fun. Now I need to think how I can punish his character without punishing my player. I would rather not drop NPC vengeance, as rest of my group could get even more relentless seeing there are no consequences of their actions.
Background of this situation:
Game is on Dungeon World system in high fantasy world. It is entirely custom made, and has not much beyond where the players currently are. Magic there is quite common and potent.
History before situation
One of my players (let's call him Bob) had a quarrel with a stablemen about quality of horses. This quarrel escalated quite a bit and finished with a guard needing to intervene. Another player (lets call her Alice) had a brilliant idea: while Bob and stablemen was gone speaking with guards, she came and casted curse on horses to look like in decay (this would hamper horse quality and help Bob in dispute). Now Bob with guards, stablemen and crowd of onlookers come to stable to check those horses.
Meanwhile, the third player (lets call him Grzegoż, he's that guy who messed up), is closing to this stable from entirely different direction knowing nothing about quarrel and curse. Grzegoż, as his character is helpful and quite compassionate offered guard boss that he will decurse those horses with small fee. Also, at the same time, guards called town sorceress, very powerful magician NPC to help with curse.
Grzegoż is a bard, but lately he was learning arcane arts and rituals. After some simple perception tests he started ritual of decursing. First time went poorly, on a second try, Alice approached him and offered help (she could help Grzegoż as she casted that curse). She can speak with different ghosts and spirits, so I've allowed speaking with those of curse. Ghosts offered deal, that she help them find another host. Alice agreed and needed to point single humanoid around (there was like hundred of different bystanders around), and in some kind a flash of genius she pointed at the sorceress. Ghosts had no choice and compelled. Also Grzegoż had no idea of this deal. Grzegoż tried second time, with "help" of Alice, and succeed partially. Expelled ghosts tried to enter the sorceress, but failed miserably as she deflected them with ease. Unfortunately for Grzegoż, she seen from where those ghosts came and assumed it was an attack, promptly freezing everyone around bind magickly Grzegoż and took him to her tower.
She lives in the town my group is now currently. She is only important mage in that town. She is super powerful, cracking entire city in half would be big problem. She is a little bitchy but generally calm and not very caring (until she's atacked of course). Her main area of expertise is ground magic, general arcane stuff and everything that could arise from being half medusa. She also helped my group quite considerable 2 sessions before and offered some more help in exchange of some adventuring favors.