幻 is a bound morpheme (b.f.), meaning it only appears inside compound words, never alone. It contributes the sense of 'unreal, imaginary' in words like 幻想 (fantasy) and 幻觉 (hallucination), and 'magical change' in 变幻 (to change unpredictably). When you see 幻 in a word, it signals something illusory, shifting, or not real.