How loopy are we talking about here? According to baseballsavant he's thrown a knuckle curve for 18 pitches of his pitches, roughly about the same frequency as the fastball, and it's averaged 79 mph, as low as 77.
From watching Stripling before he usually throws his fastball around 90-92 with his knuckle curve around high 70s and will mix in one or two other secondaries.