As you have noticed, there are several event quests in Arcadia where the NPCs who give these quests have text errors.
For the meantime, until this issue gets fixed, we have translated what these errors mean.
Before doing anything, ,several NPCs will offer to exchange coins (event or gold) for small event bags. Know that you can only do this for some before completing their quest (s); others you may have to complete the quest in order to purchase their bags.
Another thing to note is that all event NPCs are not necessarily present on the screenshots below but their sentences are identical to others and you can find what they say quite easily with the error number.
For the quest "Scary Box", you are asked to find two companions to validate it. Here are the mascots that can join you to validate the quest: PotPoury, Ellie, Huji, Chen, Aliet Yami Bunny.
PotPoury and Chestnut
Pets: Senai, Huji, Ellie, Cher, Xiaoman, Yami Bunny, Potpourri, Chestnut, Ali
Starlight Pack: Fina, Stern, Duet, Rita, Azusa, Kitsune(Koharu), Nalali(Nalani), Lenna, Aflallo, Zaro
Star Shuo Pack: Samuel, Levi, Duo, Sakura, Alice, Gaia, Aryn, Luna, Belle, Claire, Melody
You can find Alpaca coins in the reward chest by making daily arena queue
NEW PATCH HAS REMOVED THESE EVENT QUESTS IN EXCHANGE FOR NEW QUESTS