Hello,
Although I visit this wiki quite freqently and I love One Piece, this is my first time doing a blog so I hope it's not out of place. And if this has already been theorized or used in another blog, then it should be taken down since I don't want to "revive" an old topic. I just read the recent manga chapter and while they showed Donflamingo's face - they didn't show his eyes and Oda seems to always show him wearing his glasses or not showing his eyes - even when he was younger. It's a big mystery so, I got a crazy theory - what if Donflamingo is actually blind or doesn't have any eyes.
Now, I'm sure you're thinking "Well, that's stupid - look at what he has done" but my theory points mainly to two things - first, his Devil Fruit. We have seen that he can create invisible strings to either control people or use them to make it look like he is jumping in the air. We have even seen that he can use his strings to cut anything and to repair his internal organs for a brief moment. Seems like he can do anything with this Devil fruit unlike some others like Kaku and Bellamy. But what if he was able to use his strings to send possible signals or uses them in a way to "feel" things (I know some people will take this the wrong way) so therefore, he knows what he is seeing and therefore, can strike. Now, the problem with this is he would have to have millions of strings out there to be able to see the world but we saw what his Awakening powers are capable of and he might have had them even before he was officially introduced. It might be possible that he has millions of microscopic strings that he has all over the world that relay signals to his mind and therefore, he knows what's going on - similar to a wireless/Internet network where he is the main server hub.
The second party of my theory is similarly based on the Marvel Comics hero - Daredevil. Daredevil has pretty much always been blind (save for young childhood) but he has heightened taste, touch, smell and sound and we know Daredevil has a form of internal radar that lets him see differently than most. Although we know Doflamingo didn't burn his eyes by acid like Daredevil (unless he was off page) - it might be possible that his strings have some other ability that allows him to see his surroundings differently than most, again with the "feeling" aspect or sending signals.
Now, I know some people might say "Well, if your theory is correct - how did he not see that Sabo had taken Luffy's place in the Coliseum final match?" or "Well, if your theory is correct - how did he not see that Ricky was Riku under that mask?" Well, maybe strings are afraid of dragons and the mask was made of Sea Stone - I don't know and I can't answer that because it's just a theory and it probably is false. But it would be a nice plot twist if that is the case. I don't know if Oda will reveal it and I certainly he does because just like with Sabo before, we need this eye mystery solved.