While I'm distracted by whatever massive paradox this must be causing...
(Actually, since all three are from different universes (kinda, spit of regular who turned to dragon and clockwork messes with that logic a bit), there is no paradox occurring. We're safe from that.)
Now I'm suspecting you opened that rift because you were bored.
(I find this mildly insulting. That is for shenanigans. LET ME SHOW YOU WHAT I HAVE DONE IF I WAS BORED! (I'm not bored right now, just making canon what would have happened if I was bored, because I took your statement as a challenge.))
I watch as the cardboard box returns to earth, and combines with all the other cardboard boxes on the planet to form a massive sphere that launches into another dimension that somehow manages to maintain heat and light without a source. Before that, however, based on sounds inside, the inhabitants are scattered throughout the entirety of the structure. All who are outside the box within my visible range are sucked in. I do not notice wherein they go, because I am busy trying to hang onto Nepeta, so that I at least am nearby someone when I enter. It is unsuccessful, and we both enter at different points. A massive rush of air goes into the box, signifying that the box has gained enough interior space to have all its interior dimensions be large enough that a dragon could comfortably fit inside, with the air pressure optimal for habitation. The interior walls change to a metallic substance with the same appearance as cardboard in order to prevent air leaks, and the 'doors' in the shape of large cardboard box lids appear to have a method for sealing off in case of 'hull breach'.
With nothing better to do, I go searching for Nepeta, who is the only person I have a rough idea of their location.