I did Ultimate Royal Jelly and Ultimate Snarby today and noticed that a new mechanic was added in the fights: the black slow field
I also saw a picture of this in Ultimate Vanaduke, and I assume that it is on Ultimate Roarmulus. I love the idea behind it, but I feel its execution is poor in some areas.
For those that did not notice what the field is/does, it is a large black grid that greatly reduces movement speed of knights inside of it. It has a core that can be hit to reduce the size of the field until its gone. This is a fantastic mechanic, and it adds a new and unique element to bosses. The problem however is what comes next. After a short period of time, the field comes back at full size instantly. I feel that this can lead to many cheap hits from enemies. This was particularly infuriating on Ultimate Snarby, as I was running from one during a long bite charge only to be instantly slowed and bit.
Therefore I see two issues with the slow fields that should be addressed: size and respawn
Size:
Royal Jelly - I actually didn't have much issue with the field on RJ. The size was large enough to be a concern, but small enough that you could squeeze past it even at full size.
Snarby - The size for this fight was horrible. Combined with all the briars around the room, there was practically no room to maneuver when the field was up. Having two fast Snarbies chasing and biting at you, while having to dodge spikes and chasing silkwings made this awful. This is a battle where you always need to keep moving, but the slow field makes that very difficult. It made the fight feel unfair and cheap.
Vanaduke - From the image I saw, this could be an annoyance or a massive nightmare. It depends on how the fight is intended to be handled. With a well coordinated team that uses Shivermist/Blitz and takes out the zombies and slags first, this slow field won't be too bad. However with a less methodical and precise plan, the slow field on Vana would be absolutely terrible. I don't see anyone beating Ultimate Vana without dieing several times as it currently is, unless the team uses Shivermist/Blitz.
Roarmulus - I don't know the size of the field on this fight if there is one, but Ultimate Roarmulus was too easy last time I did it, so it would likely not be that bad. Movement is the least important for Roarmulus out of the bosses, so I'm not concerned about a slow field on it.
Respawn:
The instant respawn of the field is the key culprit. I propose two solutions to make it more fair. First: Cause the field grow back to its full size over time, rather than instantly after a set time. This way players would still need to hit it often, but they would not get hit with an instant, unexpected slow. Second: Add a timer over the core to show when the field will respawn. This would let players know when they need to start running to the edge of the field to stay safe (think phase 2/4 Vanaduke).
There is a Slow Field present on the Roarmulus battlefield, and it takes up nearly all of the space inside the walls. Though, like you said, it's not much of a concern here considering movement isn't nearly as important as in other boss fights. Regardless, I would enjoy seeing these Slow Fields being toned down a bit in some way or another. The ideas you mentioned would both work great; perhaps for the over-time restoration of the field, we could have a couple seconds for every growth notch? So you could shoot it down to minimum, then it would grow up a notch every 2 seconds until it reached maximum size.