I keep talking about Seatone Bullets. BUllets in One Piece are nearly always round balls, not the pointed modern day ones that look like Bullet Bills from Super Mario Brothers
Don Krieg had "dart guns" that literally shot "darts" and they wern't as fast as a bullet anyways. And besides that(DOn Krieg had everything noone else uses for some reason) all the other real bullets are like tiny cannon balls anyways.
Anyways obviously the good doctor uses Devil Fruits and Sea Stone in his studies. That is probably the usual testing for him. So I always suggested Usopp making Sea Stone bullets for use vs DF users. Like for example Enel would probably try to take it, since he's "invincible" anyways, and usopp would just embed it into him and make him weak.
Honestly any Logia user who hasn't trained themeselves to Crocodile's level of mastery and reflexes would have a chance to have it embeded in them. And thinking about it, if Enel wern't so cocky or Crocodile had Enel's fruit, honestly it would be the end if Crocodile has that power. He would, in fact be invincible, even to Luffy.
But on the topic of the good doctor, he'll obviously be a boos at some point. or the boss' assistant who is totally freaky and does something strange. Or for all we know he's a person who's just like Luffy in attitude occasionally. Or some other weird thing that probably happened becaus ehe's a scientist or from an experiment, or a weird habit like Gedatsu. Even with these broad possbilities we knowm almost any semi-good write can shatter them all in one shot, and Oda could probably mop the floor with all the theories in a few lines of dialougue.