Tiefling IRL

Nothing in the spell says they don’t. By contrast, Wild Shape

Your game statistics are replaced by the statistics of the beast, but you retain your alignment, personality, and Intelligence, Wisdom, and Charisma scores.

Also, a pile of dust doesn’t have a stat block because it’s an object. It’s not even sentient. But if you really really want to play as a lifeless pile of dust, knock yourself out.

I would argue that by this logic, your ability scores also fall to 0, killing you

Ooooh I’ve seen this movie!

Even with shield and blade song, you’d need a 19 base AC