Reading over different questions about 'Mirage Arcane', I've come to what I believe is a fair understanding of what the spell can do, but I'm left with a few questions. So far, my understanding of the spell is this:
The spell can create formations that can be interacted with as if they are real (See: https://twitter.com/JeremyECrawford/status/709549372875218944)
The spell cannot create deformations that can be interacted with as if they are real (See: Can I get creatures stuck in the ground with Mirage Arcane + Illusory Reality?)
Under the right circumstances, illusions created by 'Mirage Arcane' can cause harm (See: https://www.sageadvice.eu/2018/06/03/if-i-used-mirage-arcane-to-transform-a-lake-of-water-into-a-lake-of-lava/)
Now, to quote the spell:
The illusion includes audible, visual, tactile, and olfactory elements, so it can turn clear ground into difficult terrain (or vice versa) or otherwise impede movement through the area.
I am assuming that this means that with regards to speed, 'Mirage Arcane' would be able to create normal terrain from difficult terrain and vice versa such that the original terrain is not accounted for with regards to speed, only the illusory terrain. Is there any RAW or RAI that conflicts with that interpretation?
But more to the point: What damage type is damage caused by interacting with the terrain, if damage is caused by some means?
For example: I have before me an empty, flat field. I create an illusory hill that rises up 100 feet and ends in a cliff. I push my friend off the cliff. Given we are actually 100 feet in the air, supported by the illusion, he should take bludgeoning damage from the fall as per normal, correct?
Now lets suppose I have the same field, but this time I create an illusory cliff at the same level as the field that drops 100 feet down. I push my friend again. In reality I just pushed him from one spot in the field to another a few feet over, but for him he "fell", so does he take damage? If so, should the damage type be bludgeoning or psychic, similar to 'Phantasmal Force'?
Similarly: If I burn my friend with illusory lava in that same field, does he take damage? If so, fire or psychic? If it does not cause damage, but instead causes phantom, illusory pain as if one were taking damage, would this call for a concentration check against casters concentrating on a spell?
I don't want to shunt the power of a 7th level spell, but being able to move as if a valley/mountain wasn't present (within the spells bounds of course) or potentially devastate an entire army with illusory lava/water seems a bit much for illusion magic, even 7th level.