So, debilities. The rules as written say: “You can only have each debility once. If you’re already Sick and something makes you Sick you just ignore it.”
Am curious why that rule is there. It seems like an obvious option to interpret a vampiric attack, for instance, as inflicting the weak debility, but it would be strange if a vampire can’t affect you twice. Or, say, each day in the nonEuclidean plane of Madness, you grow increasingly confused. In general, if you can normally have a range of modifiers for ability from -3 to +3, why shouldn’t debility be able to stack likewise?
Descriptionwise, it might be boring to just stack “take another -1 weakness”, but you don’t have to do that – you could presumably describe increasing pallor, and rubbery legs starting to buckle under you, and so on.
Does that sound like a bad idea?
Being increasingly confused is covered by the fiction and the moves it triggers. Consider this:
GM: “After days on the Plane of Madness all the people start to look the same, like strange optical illusion cutouts that don’t quite make sense.”
That fiction makes triggering moves different. For example, trying to discern something about people is pretty unlikely. When they say they attack something they don’t really know who, just which shape. &etc.
Increasingly-getting-worse dangers tend to work better framed as Dangers inside a Front.
Mind-Melting of the Plane of Madness might be a series of Grim Portents with “You lose your way and become a denizen of the plane” as the Impending Doom.