@taiga_ameca, I talked to another person who helps here and they said that in order for the Day of the Dead celebrant to be willing to give you a sugar skull, you have to be near or at Friendship level for them to feel comfortable enough to give you one! That would explain why the only one you got so far was a Sims whom you were already friends with. 😉 (I was sick during the Day of the Dead Event when this challenge was actually current, and so I never got to patriciate in it. I only got the skull collection and display case through cheats.) If you try to ask for a sugar skull too soon, they wont give you one. And to make it easier to find the DoD celebrant, just pause your game after you get a message that a celebrant is in your neighborhood, so you can look around it and find them! Once you do find them, queue up a several greetings or interactions just in case the actions time out while your Sim is trying to walk to them. 🙂
For a long time other people would say that using cheats was the only way to complete the collection if you didn't participate in the DoD event.☹️ However, at some time since I last played a house with a grave on the lot, they added the ability to do the challenge! :eahigh_file: I'm glad they did this! 🥳 But I don't remember them ever mentioning this in the patch notes, so I don't know when it became available! 🤨 Sorry that my information was a bit out of date. 😳 But thank you for asking this question, else I would never know they had made the challenge available again! 😇
Happy Simming! 🥳