@Razh:
I think in order for his Shambles to work, enitre Room should have the same atmosphere. For example, he can only move a person from air to air or from water to water. He can't teleport someone from air to underwater or inside a wall or something.
There's no reason why he couldn't create Room and use Shambles underwater, the same way Van Der Dekken used his ability.
I prefer, as someone else's said before, the theory that he can't go around shambling things he can't even see. Like, he had to scan the G-5 marines to see that they were carrying mini-denden mushis, and after that he shambled them. He shouldn't be able to "guess" where a fish is and shambling it with Dofla. And, as you say, if he could shamble someone with the "inside" of a wall or with a gallon of ocean water, he'd be absolutely invincible, no questions asked. He could be facing all 3 marines + Sakazuki at the same time, and he could just shamble them into the ocean without even bothering.
Let's just assume there are some limitations, ok?
@Lady:
If Hody Jones could tank Red Hawk (granted it was with performance enhancing drugs that stacked and he kept having to take them after Luffy damaged him) Mingo should be able to tank it no problem. But Luffy's fights with the main villains are never over quickly, I expect a lot more damage to go around, we haven't really seen Luffy's durability tested in the NW.
In Hody's defense, his biggest (and possibly only) merit was being a tank. Luffy complimented him on that. He just. . .tanks stuff. And even with that, the Red Hawk DID a number on him, since he had to swallow tens of pills after that attack to recover from it.
It's weird people are trying tu make it look like starting with a Red Hawk is no big deal, when it kinda is. For all we know, this could be among the strongest post time skip attacks this side of Elephant Gatling and Grizzly Magnum, and he landed it right at the beginning of the fight. That's quite the novelty concerning One Piece big boss fights, cause he usually starts landing punches and kicks and not haki imbued gear second exploding flaming fists to the stomach. . .
@baby-boo:
Concerning Law shambling people under water …
... unless I am mistaken, but isn't Law only able to switch places with himself? He's moved objects within his room, he's cut them, but he's never switched two different things or people unrelated to him, to my recollection. When Fujitora held him down, he switched places with a rock. Then he threw a log in the air, switched with it, and then switched places with Doffy again to save Sanji.
For Law to shamble someone into the sea, he would have to be in the sea to begin with, and that wouldn't really work out too well.
Well, the "original" shambles attack actually moved and combined body parts around, so I don't know if he's limited to that.