In theory a lot of these things are going to be self-contained, but there's a bunch of things that I think I'm going to want to use/make that I'm going to reuse a lot. This is where that's going to get posted. Hopefully these are all just small linkable ideas that I can link inside a stat block rather than rewriting a hundred times.
The creature have feathers covering most of their body. They gain 1D of armour to their arms (or wings) and legs due to the padding the feathers can apply. However, they can easily have those feathers damaged. If the monster is struck in the wing or the back/legs they have a chance of their pinions or tail feathers damaged. When those feathers are damaged they cannot fly. Roll the DoF, on a 6 or better those feathers are damaged, the attacker can spend additional successes to increase the DoF (before the DoF is rolled). The pinion feathers take two months to regrow, the tail feathers only take a month to regrow. They can also be regrown with a Minor Miracle.
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A Burning Wheel Monster Every Week