Fiduspawn (possibly a corrupted portmanteau of fetus + spawn) is a card game on both Alternia and Beforus, of which Tavros and Rufioh Nitram are both players. It appears to draw influence from real-life monster collecting games such as Pokémon, as well as the Alien series of science fiction horror films.
Unlike most card games on Earth, a game of fiduspawn involves actual monsters. A "match" is kickstarted by the dispatch of an oogonibomb
(likely from oogonium, a kind of cell in the development of certain female fetuses, and bomb), which hatches into a creature similar to Alien's facehugger (called a “fidusucker”). This creature attaches itself to a “HOST PLUSH” (and then proceeds to scuttle off), which then explodes open into a monster. This monster then performs spawntechs for the player, and can gain levels and be bred. The “manufacturer recommends that you only hatch some” to avoid having “way too many fiduspawn crawling around”.
Unlike Pokémon, in which a monster is always born in its least developed form (usually called a Baby Pokémon), fiduspawn seem to be spawned at different stages of development; while Tavros is able to spawn a “Horsaroni”, Meenah Peixes instead spawns a “Horsaponi” which must be trained into a Horsaroni. Also unlike Pokémon, more developed forms of fiduspawn “gain no measurable advantages in combat” and change little in appearance, only growing “slightly bigger”. Adversely, and reflective of real-life animals, more developed fiduspawn require more feeding.
Bronze Page ♫ from coloUrs and mayhem: Universe A references a troll TV program named after or relating to fiduspawn, possibly implying the existence of an animated adaptation like Pokémon's. Lyrics relating to a land where friends defend one another (evidently someplace away from Alternia) and to a character who fights for the rights of fairies may in turn relate to the content of fiduspawn or its adaptations.
In A6I3, Horuss Zahhak calls fiduspawn (or "“Fiddlespoon”") one of the “foreign card games you” (Rufioh) “seem to like”, implying it may be of Alterniasian origin.