I chanced across a question someone else asked about the Ranger's move Unnatural Ally while looking through the Dungeon World GitHub's issue tracker. Asking a question about the game is arguably not a design issue, so unsurprisingly it's gone unresolved since 2012 Maybe we can close this one out then…
The question they posed is this:
For the Ranger's Unnatural Ally advanced move, does the existing companion become monstrous or do they gain a new, replacement, monstrous companion?
If the former, then they should probably describe what happened to it, right? Does the boost to Ferocity and Instinct stack with whatever they had before?
If the latter, are Cunning and Armor just based on the creature picked? And it knows all the tricks the old animal knew, plus a new one?
That question is referring to this 6–10 Advanced Ranger move:
Your animal companion is a monster, not an animal. Describe it. Give it +2 ferocity and +1 instinct, plus a new training.
My initial reaction to reading the question was to breezily think that it would probably be obvious with a re-read of the move and some working knowledge of Dungeon World, but actually I find myself uncertain at the correct answer.
My initial assumption was that “of course” you have the same animal companion — but the broad discretion the move gives the Ranger to describe a completely different sort of creature makes that hard to swallow. What, does the Ranger wake up one morning, look at his owl, and go, “Good morning, Archimedes! …Goodness, I never noticed that you're actually a manticore! Well then, silly me.”
Conversely, the move also says “Give it +2 ferocity and +1 instinct, plus a new training”, which wording implies that its your existing critter companion.
How does this move work, both regarding the mechanical issues in the above quoted question, and fictionally (which are inextricably intertwined, this being Dungeon World)? Does it make the Ranger's existing animal companion suddenly (or suddenly revealed to be) a monstrous creature, or does it replace the Ranger's existing animal companion? Some middle ground I'm overlooking? And whichever it is, how do the monstrous companion's stats work in that case?
Or does this “simply” fall under the usual “ask the Ranger how their class works” GM manoeuver, so that you just follow that fiction to an ad hoc, per-Ranger reconciliation of these conceptual and mechanical conflicts every new Dungeon World campaign? Even if that's the answer, that leaves me (and I imagine others) right back at the beginning, tripping over the apparently contradictions and wondering how these can be at all reconciled with a good fictional explanation.