Yeah, the campaign I’m running (a modified Ghosts of Saltmarsh) has got a lot of underwater combat. Any tactician worth their salt is going to take advantage of the three-dimensional underwater space, but roll20 is not well set up for that at all. A player in a recent session made excellent use of Control Water to create an underwater whirlpool, trapping a half-dozen enemies in a 5’ diameter column of water. Representing that on the map was a giant pain in the ass, and I was super glad when the barbarian got sucked into the whirlpool and turned it into a high-speed blender.
I’d have probably just drawn a 5’ diameter circle, with an arrow pointing to it and then a list of who all was in it.
(I assume that you can free-draw circles and arrows in these programs)
Oh, I had a whirlpool graphic ready to go, complete with 50’ blue aura to show the zone in which creatures were pulled into it. That was all ready to go. The complexity was that some enemies were pulled directly into it, while others were 5’ away. I ended up scattering the “inside” enemies in the cells around the whirlpool, and putting the 5’ away ones 10’ away. But it was clunky and ugly, and it was very satisfying to watch the barbarian smush like three of them in a single round and eliminate them from the hot mess.
The biggest spatial reasoning fail I’ve seen from my players involved making tea in a kettle. Not in game, in real life. I’m legitimately lucky they didn’t burn my house down.