I touched up on this briefly in my initial reply to this topic. I generally agree.
I feel like the boss should be changed to reflect the gimmick of the zone. Namely, the fact that the goop bounces. Either have the balls bounce around after Eggman launches them, or redesign the entire boss around the new goop mechanics. Perhaps making use of the idea of being able to walk on ceilings while inside goop.
A quick note is that I don't mind the inconsistency, but in this scenario I understand why people would and wouldn't mind it being looked at.
Personally, I'd think it could be neat if the boss was reworked with slopes in mind, rather than JUST bouncy goop- I've briefly messed with the idea in zonebuilder before, but the rocks falling in Arid Canyon, as they should, actually bounce differently on slopes- Perhaps the boss could be reworked to be stationary and at the top of a large, curved hill-like spire.
It fires bouncing slime in the direction of the player at 3 pre-set levels, each causing a different bouncing arc toward the player- the bounce-slime could have a bomb inside of them to show how it targets the player, and how it hurts you.
Afterword, it could maybe do one of two things-
1: It takes a moment, before firing a solid stream of goop at you- just like old Brak's sticky goo, but with the current Egg Slimer's hurt-goo. This does not bounce, and is simply a trail the player must outpace and evade, with the boss occasionally stopping to fire a single bounce-goo straight at you, which trails you for a bit to stop players from just inching along the edge of the arena to limit goop spread- probably 3 bounces.
2: It could fire three rings of goo into the air, which encircles the arena- This would reference the current version of the boss, but the three rings of goop would be in pre-set locations- making them recognizable, but also still become a hazard.
For it's phase 2, the boss itself could surround itself in goo, and bounce after the player, just like it does now- but it leaves a large splatter of goo wherever it lands rather than a ring of goo, and hitting it sends it bouncing around for a few seconds, before it continues the chase- This would be it's last 3 hits, IMO.
This would cause players to have to mess with slopes some more, in tandem with more mobile threats, creating a boss that tests players on slope usage, as in recognizing how they effect physics and playing around with them (For example, jumping off a steeper part to get some speed away from one of the attacks), as well as having them perform a new interaction with the major gimmick as a threat.