The circling underwater would be incredibly cool, though I imagine it will probably be like you said, a puddle appears, the pokemon drops- the puddle stays their ominously until next turn and then the pokemon reappears to attack. Same with Dig probably too.
I can't remember who it was that said constant weather- but that would be amazing, Sandstorm and Hail especially! I'd kind of like another weather condition this gen tbh- probably unnecessary and what not, but it would be cool. I've heard some people taking about like a 'Gale' strong wind condition, that could increase the Speed of Flying types as well as their attack power? Possibly do something regarding trapping moves.... :O what if it prevented the use of entry hazards for a number of turns? Because they are blown away :O that would probably be deemed 'broken' but tbh, Flying types could really do with some love after Gamefreak inflicted Stealth Rock on them. I won't get all meta here- tbh, I don't really play meta, but just the idea of Stealth Rock p*sses me off- because so many of my favorite pokemon like Scyther and Crobat get a big ol' chunk snatched from them.
I dunno, I jsut some thoughts.