Illusions

An illusion is a magical effect that creates a false sensory experience — an image, a sound, a smell, a phantom creature, or a combination. Illusions are a category of Magical Effect, typically created by spells from the Illusion school.

General rules:

• An illusion is not real. It cannot deal damage of its own, lift physical objects, or interact with the world in ways that require substance.
• A creature that interacts with an illusion physically (touching it, trying to walk through it, attacking it) immediately recognizes the deception — no check required.
• A creature that suspects an illusion may use an action to study it and make an Intelligence (Investigation) check against the spell save DC. On a success, the creature knows the illusion for what it is. Other creatures who witness the disbelief may also become aware (DM's call, often a free action).
• Once a creature sees through an illusion, the illusion becomes faint and transparent to that creature only. Other observers continue to perceive it normally.

Common illusion spells and their interaction with disbelief:

• Minor illusion — a small sound or image; disbelief is usually trivial under scrutiny
• Silent image, major image — larger visual illusions, can include sound and other senses at higher tier
• Mirror image — duplicates of the caster; attack rolls determine which is real per attack, not a disbelief check
• Phantasmal force — affects one creature; failed Int save makes the illusion feel real, including dealing psychic damage

Limits:

• Illusions cannot exceed the senses specified in the spell description
• True sight (the spell or the creature trait) sees through illusions automatically
• Blindsight bypasses purely visual illusions