What does the speaker mean or imply with the intonation on "online" at 0:31 around? A negative and doubtful query? Does the intonation pattern on "online" completely fall at the end? Or, does it slightly rise at the end because it occurs before a pause - intonation unit?
As pointed out in the comments, the speaker's tone, at least to me, seems to express derision and/or mockery of the concept of an online party.
A party, of course, is a gathering: an event where people come to a location in order to enjoy themselves with other people. When such an event takes place online, some elements of the event can be more awkward: everyone is in the same "room," so to speak, where chatting with a select group of people is much more difficult; people are prone to technical difficulties which limit their ability to participate in the event; people cannot share food or beverages with others; and so on.
Since the pandemic began, events have had to adapt to online environments, which, as I'm sure you've experienced, have a hard time surpassing that beloved human interaction. Plus, with the party being a murder mystery party, one would seemingly have to put on a costume only to sit in front of their computer the whole time. Obviously, this is not ideal. Some people, like the speaker, also probably find it awkward and/or strange to have such an event online in the first place.