Although I have argued strongly against magic answers to questions that are not about magic, I would like to see questions about magic. Provided they are framed in a way that allows for clear, definite answers, I welcome questions on fantasy, alternative physics, and self consistency of asserted magical properties of creatures/cities/geographical features/...
As TimB points out in a comment on the question, it wouldn't make sense to ask the biggest possible creature question in a magical setting, but if you already have a large creature that you assert can survive at that size due to magic, you could ask what consequences this might have for the surrounding environment, landscape or climate - that would be a scientific treatment of an impossible creature.
Alternatively you could ask purely about the self consistency of magical rules. If a magical river turns everything that touches it into gold, how should the effect end where the river meets the sea? Should there be a reef of dead golden fish marking the line along which river becomes sea? What additional magical effects will be needed to prevent the river clogging up with golden leaves at the end of each summer, since they cannot be carried by the current like natural leaves?
I include alternative physics here because I see it as "science based magic" - fitting somewhere in between. For example, you could ask about a universe where the gravitational force is 10 times stronger. In a solar system where the Earth is much smaller, so the people on that Earth experience the same gravity as us, how would that universe's higher gravitational force affect the appearance of the sun and moon in the sky? How would it affect the tides, seasons, days...? Would the life cycle of the sun be different with the increased gravity? I overlap this with magic because the purely scientific answer might not be what the asker is seeking - a world that looks so similar to ours might be unrealistic.