Being a clone of Donatello, Dark Donnie is the smartest of all the clones. He doesn't always act like it though, being snarky to their leader Dark Leo and fighting for food like the rest. But that doesn't mean he's not intelligent; he is presumed to be the creator of the Terrorpin, their ship that is the equivalent to the Hovershell, and probably all of the other gadgets he is seen using (e.g. the giant magnet and smoke bombs in Bad Blood)
Out of all the clones, Dark Don is the one with the least resemblance to his counterpart. His brothers all have a similar head and face shape to the actual Turtles, but Dark Donnie does not.
Dark Don does not seem to own a weapon though. He relies mainly on his analysis of his opponents in a fight, finding a pattern in which he can block their attacks with his metal wrist guards as well as openings for him to attack. In fights, he'll often end up using his long tail (being that he is the only one of his brothers to have a tail) as a weapon as well. He is also shown taking advantage of the appendage in other situations too (grabbing food from his brother's hands as seen in DNA is Thicker than Water).