I think a slo-mo when defeating an elite monster (or perhaps just new monsters when you defeat the first one) would be extremely cool; however, it should be allowed to be toggled off for speedrunner's sake.
I also feel a "day/night cycle" is too simplistic; Having phases or comets (this is juice galaxy after all) that could happen at random or non-random intervals could be very nice. Having it be comets could also give a greater sense of progress after defeating the creator with it doing something to the pollywogs (werepollywogs?) that couldn't happen before then. (really glad you talked about the day/night cycle cause it gave me the idea of comets)