The "proper feature" for a Rio Da Yung OG and Flint-style type beat would ideally be a rapper who embodies the characteristic of the Michigan rap scene .

: Flint tracks often prioritize long, uninterrupted verses over catchy choruses.

: His slurry, nonchalant delivery creates a unique dynamic over the fast-paced, frantic energy of a Flint-type instrumental. Key Characteristics of a "Proper" Feature

: Starting sentences mid-measure or finishing them after the bar ends.

: As Rio's most frequent collaborator, Mike’s gravelly voice and "shouting" delivery perfectly complement the heavy bass and piano loops of Flint beats.

: Lyrics often involve vivid storytelling about street life mixed with unexpected, funny punchlines.

If you are looking for a specific artist who has a song actually titled "Free Stackin" or something similar, it likely refers to a local Michigan artist or a specific remix within the Flint rap community.