So in a recent arena game i encountered a strange interaction involving The Darkness, Unleash the Hounds, and Spreading Plague. My opponent played The Darkness early on, thus occupying one of his spots with a dormant minion. Unleash the Hounds recognized this, and created a hound for the enemy minions including The Darkness, which was still dormant. However, on the following turn my opponent played Spreading Plague, which did not recognize The Darkness as a minion, and created an extra beetle despite having an equal number of minions with the dormant Darkness included.
Is this a bug or is the wording on the cards different enough that this is the proper function?
Unleash The Hounds does not account for Dormant Darkness when it creates minions and the same goes for Spreading Plague. Dormant Minions do not count for those cards. You must have missed something. Regardless, Spreading Plague will always create one Scarab as part of it's effect and after that, any additional ones only appear if you/your opponent has more minions than you do.
The Darkness is a very unique card so there are questionable interactions with it. (E.g. Glinda doesn't give it echo because on paper it is a minion but the game handles it as a dormant/permanent thing like the Warlock Quest reward)
The "adjecant minion(s)" and "have X minion(s)" interactions are all clean, right?
The interactions work as if there was no minion there. Think of is as there being a rock in play. That rock cannot attack, it cannot be buffed or targetted, it does not count as a minion since it is not a minion, it is a rock. If you play an Adjacent effect, it will do nothing to it. If you play Flametongue next to it, Flametongue is next to a Rock. It doesn't but the rock, and it also doesn't buff the minion on the other side of the rock because Flametongue is adjacent to the rock, not the minion.