[Intory]

in my experience, i have not read very much in the Pali suttas that mention "illusion", apart from the Phena Sutta, which emphasises the transcient (impermanent) and ultimately insubstantial qualities of the five aggregates, that is, the five component parts that make up a human life

so possibly a reading of the metaphors in the Phena Sutta may help clarify what 'illusion' is

to me, the Phena Sutta seems to focus on the illusory nature of mentality (rather than an illusory quality of the 'external' world)

to me, the Phena Sutta seems to challenge the common notions of 'solidity' & 'substance'

kind regards