This no longer simply unlocks by breaking the piggy bank
After fixing the robots, the Kiryat priest will give you a letter, which you will bring to Arrowsmith in the bar. He will give you his hammer in return, which can be used to break the piggy bank in Thor's home. This will give you a coin, which can be stuck up the carousel horse which is located in the Hiding place area of the map. This opens a hidden chamber. Inside, you will get a tape of a fungi fish ( don't ask). Now you can walk to the priest in the temple Pentatonica to get the weapon in exchange for the tape.After that, you can actually challenge the viking guard for a duel, the guy downstairs in the bar area. First you have to attempt to steal from the unicorn box, you have to talk to sergio in the far left corner of the bar. He wants a cocktail which needs the unicorn stuff. That will allow you to take the contents , then try and leave. This will initiate the duel.