Do objects/magical effects have to interact with Mirage Arcane?

Question

The Mirage Arcane spell says:

Creatures with truesight can see through the illusion to the terrain's true form; however, all other elements of the illusion remain, so while the creature is aware of the illusion's presence, the creature can still physically interact with the illusion.

This similar question discusses the interaction between a character and the illusion as being optional if the character has Truesight. Does this optional interaction apply to the following:

• Objects attempting to pass through the illusion (i.e. a character wanting to shoot a ranged weapon through the illusion)?
• Magical effects attempting to pass through the illusion (i.e. does a caster have a Clear Path to the Target for a spell effect)?
• Does the ability to perceive through the illusion apply only to creatures with Truesight or can characters with a blindsight type ability like a Rogue's Blindsense allow the character to ignore the illusion within their range?

Answer 1

Yes. Objects, magic, and creatures interact with mirage arcane even if they know it's an illusion.

Truesight allows only vision into and through the illusion.

Truesight does not change any other interaction aside from the visual, as "all other elements of the illusion remain". That means of the "audible, visual, tactile, and olfactory elements" only the visual are pierced by truesight.

Those with truesight "...automatically detect visual illusions and succeed on saving throws against them..." Mirage Arcane does not have a saving throw associated with it.

Perception of the illusion does not negate the other effects of mirage arcane.

Save for truesight, there is no provision in the spell's description that allow for a creature that knows it's an illusion to opt out of the spell's effects. Even with truesight, only the visual elements are optional.

Projectiles still interact with the illusion

Objects attempting to pass through the illusion (i.e. a character wanting to shoot a ranged weapon through the illusion)?

An arrow would still be stuck in a tree or shack created by the illusion. Other illusion spells such as creation also create elements that can be interacted with physically.

Mirage arcane still affects path to target.

In the same way one cannot target through a window pane, there isn't a clear path through the mirage terrain even if the caster can see through it. There's a relevant question about casting through transparent things.

Blindsight & blindsense

The spell's text only provides for truesight to see through it. As the effects are also olfactory and tactile, those could be use to narratively account for blindsight not being able to penetrate the effects.

Blindsense reveals hidden or invisible creatures. Mirage arcane does not add creatures nor conceal creatures, so the ability does not operate on the same targets as the spell does, and would not indicate the presence of the illusion.

Might be able to detect the presence of the illusion's facade.

At clever DM might find a way to convey further information to those with senses that could ostensibly detect the terrain beneath that affected by the spell. For instance, a creature with tremorsense might notice the sensation beneath the surface of the illusion does not match what would be expected.