Though most people I see seem to be complaining about the Jelly Palace being too hard, I disagree. It used to be a pinata fest and now it's actually challenging. Jellies are actual enemies now with their own unique types of attacks to watch out for.
The Jelly King himself though is a fight that's become extremely hard for one reason: the fact that each add he spawns can all attack you from any direction, ranged, continually, and impossible to see, is just too much on top of the boss's own attacks and all the little jelly cubes around him. You just can't get attacks in, especially not with a slow weapon, and your shield will get shattered rapidly (yes, even pierce/normal ones).
My suggestions are to either lower the range of the jelly cube's underground spike, or if that would nerf them too much beyond the JK, just reduce the rate of his adds, big and small alike. Now that the jelly cubes are actually formidable opponents in their own right, he doesn't need to summon quite so many of them to pose a challenge.
Not only that, but the spiked jellies can land attacks through walls. No other enemy does this aside from Gremlins through gates (which really needs to be fixed as well) and people have died to an enemy that's supposed to be out of range and unable to attack. In Depth 16 especially this becomes an issue when players decide to wait by the party button to take out the turrets are assaulted by spikes popping up underneath them by enemies that are out of their own reach.
But then again, I guess I'm kind of derailing this topic with a rant that doesn't really involve the JK at all..