Once you reach The Warrior’s Rest Inn in the Zwaardsrust region, go inside and you will see the green tockle right there on the bottom floor.
Upon heading to this area, you will be in a small room with a bunch of people. Speak with the woman in the top center of the room to find out that she is planning on marrying Ortega, but the townspeople seem to have gone a little crazy. The townspeople seem to have gotten crazy, though, as they aren’t exactly all too thrilled about this wedding now. She gives you the quest, An Endangered Engagement, asking you to get some Defuddle Drops. To get these, you need to head to the Altar of the Starry Skies - The Observatory, then speak with Pavo there. He will hand over the Defuddle Drops, so return to Erdrick’s Future Home to hand them to the soon-to-be-bride.
Make sure you’re prepared before handing over the Defuddle Drops, though, as you will be forced into a boss battle. The Archfiend’s Acolyte will be your dance partner here, and he can be a bit of a pain, as he is pretty much heavy on magic. He has access to Whoosh, which hurts your entire party for decent damage, as well as Frizzle, a fire-elemental spell that can hit a single target for upwards of 60+ damage. To make things even more annoying, it can use Dazzle on your party to make them connect less with physical attacks.
The Archfiend’s Acolyte can also put a single character to sleep if it does something with its eyes. This can be a bit of a longer battle, since the boss has somewhere around 700 HP. It can also be a bit of a challenge, since Frizzle hits hard at the point when you can first take it on. However, you can make things a lot easier on yourself if you can get Fizzle to land with Serena. Doing this will make it so the Acolyte cannot use spells like Whoosh or Frizzle, so its damage output will be severely nerfed. If you can keep this on the boss at all times, this fight is a lot easier.
Once you defeat the Archfiend’s Acolyte, you will be finished with this little sidestory and will receive a Gold Rosary as your reward.