@10ebbor10 In regards to air, air is highly compressible so one could assume either that all the air is pushed away as the object materialises, or even if the air is then trapped within whatever materalises it just wouldn't be much stuff. It might heat up a bit.
On the other hand liquid and solids much less so. When you compress dirt you're compacting it's (non-atomic) particles so they stack together uniformly. You can't really compress, say, a crystalline rock. You get denser rocks mostly when rocks form with high metal content - metal ions are small where silicon/oxygen atoms are relatively large so they fit into the gaps of the crystal matrix. The positively ionic metal and negative oxygen also bind the rock together a
smidge denser.
The atoms just can't really be squeezed any tighter together - the repulsion between their electron clouds will get exponentially greater as they are forced together. If you keep squeezing a non-porous solid/liquid more and more they won't keep getting denser - until you hit a tipping point and the atomic structure collapses with the nucleus's getting packed together as tightly as they go (about a million times denser than the sun), which is what you get in white dwarfs.
You can get some dense crystalline rocks forming under high pressure, but the high pressure placed on the rocks when they form is forcing the crystals to pack themselves into a denser geometric arrangement rather than actually getting the atoms to pack closer together. This is why two mostly completely solid objects being superimposed would be dangerous, since in each their electron clouds are already interacting. In the instant of the object materialising the potential energy of the substance would go through the roof, far more than doubling. What exactly happens next is a bit of a guess but 'explosive', 'energetic', and 'bad' are all good descriptors.
So soil can be compacted, but rock can't, and bodies are ~70% water which is mostly incompressible as well. Anyway, this was all just an excuse to link a 59-second video that is mildly related -
here is video of a rock that formed under high pressure exfoliating. It's dense crystalline structure is not stable at atmospheric pressure so it expands on the surface. It's very rare to get footage of.