How to include showcased work at a conference in a resume?
I assume that your showcased work was not published in the conference proceedings either online or offline. 

If you did not receive any written acknowledgement about this showcased work in the form of a certificate, then it is not wise to write this in CV. There are many activities we do while studying, but not all go to CV.

If you have any proof for the same (in the form of a certificate), you could add the following information into your CV: 

(Author, Year, Title, Conf, Venue) e.g.

Lastname1, Firstname1, Lastname2, Firstname2, (2018) "A demonstration on the XYZ Game," in International Conference on Funny Games (ICFG), January 22-23, University of ABCD, Country. [Showcased work, unpublished]