Sure, so long as the crossover is with something you have the rights to (and since I'm assuming you're crossing over with your own comic that shouldn't be a problem) and can be linked to preferably without leaving Tapas (again, if it's your own comic, this works) and isn't like... something really at odds with the general vibe of Errant, I'm open to that.
Basically what you're probably thinking of, like a character from Errant hanging out with a character from Rise of the Heroes, is totally cool, and I'm only being fussy over rules in case somebody sees me saying "crossovers are okay" and sends in like.... Rekki with a copyright character they don't have the rights to and I don't have permission to put in my comic that I monetise (Like yes, I would love to see Rekki hanging out with fellow spikey haired fashion disaster worst girl, Catra from She-Ra, but let's keep that to social media, I can't display that on the comic itself 
).
