I am a 2018 grad, 6'2" 170lbs and throw on flat ground 80-81mph. How much more would my velocity increase while pitching off of a mound?
2-5 maybe? Depends on how linear your mechanics are.
What does that mean? Linear mechanics?
If you rely a lot on momentum towards home plate, your flat ground velo will/should suffer quite a bit (3-6 mph), but if you're rather rotational, it should only take off ~1-2 mph.