This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
The exact historical development of 蘙 is uncertain. It visually combines 艹 (grass) with 翳, but the original semantic and phonetic roles are unclear.
With no clear meaning, picture the grass radical 艹 covering the complex lower shape like a thicket hiding something unknown.
For エイ, imagine an 'A' (エイ) shaped vine growing through the grass and tangled lower parts, tying the shape to the sound.