Its vowel height is open, also known as low, which means the tongue is positioned as far as possible from the roof of the mouth – that is, as low as possible in the mouth.
Its vowel backness is front, which means the tongue is positioned as far forward as possible in the mouth without creating a constriction that would be classified as a consonant. Note that rounded front vowels are often centralized, which means that they're in fact near-front.
It's rounded, which means that the lips are rounded rather than spread or relaxed.
[ɶ] is not confirmed to exist as a phoneme in any language. A phoneme generally transcribed by this symbol is reported from the Amstetten dialect of Austro-Bavarian German. It is the rounded equivalent of /æ/, not of open /a/, and so would be more narrowly transcribed as [œ̞] or [ɶ̝]. However, the vowel formants place Amstetten /æ/ and /œ/ one third of the way between /a/ and /i/, matching the IPA definition for open-mid vowels.