@Jabra:
Well, it's a Paramecia so Oda can do whatever he wants with the fruit and it's strengths/drawbacks, but what if he simply can't create his own Doppelganger if there is too much light? That's why I said that Oar's massive body blocking the sun might have allowed him to materialize his shadow in the first place, while he couldn't against Jinbe and Doflamingo. It makes sense, after all we only ever saw him use Doppelman during the night at Thriller Bark.
But honestly, his encounter with Doflamingo bothers me a lot more than his clash with Jinbe. We could think of a ton of excuses why he didn't use his shadow against Jinbe. My favorite would be that he massivley underestimated him and thought he could go for an easy one-hit K.O. by taking his shadow (thus the scissors). But Doflamingo came with an army of Pacifista to finish him off, he had to fight for his life!
Why didn't he use his clone to escape, just like he did back at Thriller Bark?
! http://z.mfcdn.net/store/manga/106/49-474.0/compressed/OP_002.jpg
There must be some limit to his ability, that's the only explanation I can come up with (apart from "lol plot").
If Doffy blindsided him at the end of the war, he might have not even had a chance to use his clone and escape.
Also, the only person we've seen him use that clone trick on is Luffy, who is routinely fooled by tricks and gags. Doffy is a different animal.
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@King:
Haki could also be a factor too.
Also, forget what I said earlier about Doppleman. It was cloudy back then.
I love it when we can just go eh haki and sleep soundly at night. I really do.
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@Tangaroa:
True, but his zombies not being seen as unstoppable anymore would add to the perception he's weaker. And he'd be forced to fight himself more often.
I don't think Moria's zombies are particuarly widely known about though.