The 14th-level Illusion Wizard feature, Illusory Reality, allows you to make an object in an illusion real (PHB p. 118):
Illusory Reality. By 14th level, you have learned the secret of weaving shadow magic into your illusions to give them a semireality. When you cast an illusion spell of 1st level or higher, you can choose one inanimate, nonmagical object that is part of the illusion and make that object real. You can do this on your turn as a bonus action while the spell is ongoing. The object remains real for 1 minute. For example, you can create an illusion of a bridge over a chasm and then make it real long enough for your allies to cross.
The object can't deal damage or otherwise directly harm anyone.
A 14th level Illusionist is being grappled by an orc. She makes an illusory wall with major image between them, with the orc's arm passing through the illusion. Then she uses Illusory Reality to make that wall real. What happens, given that obviously from the ability text the orc cannot be harmed by this real wall appearing in the same space as its arm?
Some non-exhaustive options that I've considered:
- The Illusionist fails to use the feature. The orc cannot be harmed by it, and would be if their arm was "tele-fragged" by this now-real wall. So the ability fails entirely.
- The orc is pushed to the other side of the wall (following mechanics like those used in Wall of Force). The ability cannot deal damage or directly harm the orc, but pushing the orc out of the wall's space is not directly harming it.
- The ability resolves, but there is a convenient orc-arm-sized hole in the wall where the orc's arm is, since the ability cannot harm the orc.