I've got some questions about how this spell can be used.
You create an illusion that causes natural terrain to look, sound, feel, and smell like a different kind of terrain. This doesn’t disguise any structures or creatures in the area.Any creature that touches the illusion or uses the Seek action to examine it can attempt to disbelieve your illusion.
So... let's say you cast Hallucinatory Terrain over a pond (or maybe quicksand), and make it look like solid ground.
Does this work? Is "pond" or "quicksand" a type of terrain? Does it count as a structure?
The hallucinatory terrain feels like normal terrain. Can a creature walk on it with a pond underneath? This would give them a save against the illusion, so would they only fall into the water if they successfully disbelieved the illusion?
I like the idea of making a clever pit trap out of this.
Could you use Hallucinatory Terrain to make illusory difficult terrain? Or cover up difficult terrain with an illusion of a nice flat field, then walk over it?
How would you guys rule this?