I'd like to add that SCal is a "Super Boss" AKA A raid boss for all you RPG Rougelike players out there. It's not intended to be fought the same way as normal bosses. It's meant to be very difficult and it's not the only boss like that either.
Take a look at Ultraconyx's Void Wyvern or Elemental Unleash's Spirit of Purity Remake and you got 2 other bosses that'll test your skills the same way SCal does.
(With bullet-hell of course)
Okay, cool, great, what does this solve?
If you can't make a superboss insanely difficult compared to the other bosses before it and also keep the mechanics of Terraria itself holding strong throughout the battle, then it's not even a Terraria boss by that point.
The Spirit of Purity fight doesn't function anywhere near like Terraria's normal mechanics, as you have to get a certain mount to even prove yourself capable of even fighting the thing, which entirely removes the mechanics of movement that the Terraria player, when not using a mount, has. The boss doesn't even function on the normal health system, you have a hit counter. The arena is entirely different, the way attacks are delivered are entirely different, in many aspects it's just Touhou but in Terraria. I do not consider that boss fair to the mechanics of Terraria either, although I will say that the boss is fairly built for what it is.
But my point in saying that is that
the only way that boss works in Terraria is if you change the mechanics of how you even play the game itself.
Supreme Calamitas attempts to desperately shove both the mechanics of bullet hells and Terraria together, and for what it is, it's flawed, but salvageable, however I would
not consider it anything like the Spirit of Purity. Please do recall that the Calamitas fight is not ENTIRELY bullet hell. She will directly attack you by firing off projectiles and blasts, and will charge at you at speeds higher than we've seen in a boss up until this point. People find those segments of the fight the easiest (although still pretty hard) due to the fact that it relies on the mechanics of Terraria in an efficient, fair manner. It lets you fight this boss in a way that you're used to, but still ramps up the difficulty insanely due to the fact that her damage alone is
massive, to the point in which
you cannot afford to screw up.
Then there's the other half of the fight, the bullet hells. The bullet hell segments are built so that you, as the player, CAN deal with them effectively if you just focus and slow down. This is the part of the fight I personally get hit the least, solely because Fabsol has taken the time to actually make sure that it's possible and fair, and because the bullet hell segments are designed so that you CAN weave around the shots fired at you effectively. However, the damage they deal is still absolutely astronomical, and is hard to recover from, especially in the
first bullet hell segment.
Granted, issues do feel present, as Terraria's mechanics were not meant to be tested in this way. While you can get used to them easily, I feel it would have been better to adjust the fight similarly to the Spirit of Purity, where your movement is entirely adjusted TO the fight. However, the segments themselves do not seem that bad, as getting past them is quite possible if you slow down and focus.
See, these two things I don't have complaint with. The damage provides the difficulty, and I do believe that the changes in mechanics delivered, for the most part, are fair. The fact that your adrenaline takes a full 45 seconds to fill up, despite what upgrades you've given to yourself to lower that time, makes it so that you cannot rely on blazing through that fight and filling your meter solely over the course of the bullet hell segments. The fact that you are locked into an arena, which based on your difficulty, limits you further and further, forces you to take her on without running away, which is a tactic you can use for a majority of both vanilla and Calamity bosses.
But the hit counter ruins all of it for me.
See, when you already have her dealing astronomical damage to you with each attack, each one flying towards you faster than most anything you've dealt with before, and when you're already pressed on recovering from the damage dealt to you by timing your heals, making sure you avoid said damage as much as you can, placing a hit counter on you doesn't seem fair. If this was entirely bullet hell, sure. Then you can adjust to those mechanics entirely, and you wouldn't have to focus on dealing with her herself. This is why the hit counter system works in bullet hell games: all you need to worry about is dodging, not dealing damage. If the fight was entirely the segments between each bullet hell, then that'd
also be fine, as you are more capable of simply improving your skill in Terraria itself, to the point where you SHOULD be able to avoid taking damage altogether, without worrying about some other segment screwing you over with absolutely massive amounts of bullets.
But it doesn't work like that. You need to deal with all of them, at points it even feels like you're dealing with it all at the SAME TIME, due to the sheer amount of projectiles within the given space you have in the small arena you have. Stacked on top of all of this, you are given a hit counter that persists throughout the entire fight, which negates the point of even healing or wearing a good set of armour, as all of that has no point anymore. You will inevitably die, lowering the damage dealt to you is pointless if you're forced to try your hardest to no-hit the fight. There's no challenge or skill in making sure you can heal at the right points, because no matter what you do, you're a step closer to death.
I feel like removing the hit counter would lower the difficulty too much, of course, as the fight is built around this system. But I personally believe the system itself is flawed.
This wouldn't ruin the fight, I do not believe, though. If you applied other kinds of restrictions, debuffs, anything to the player in place of it, the difficulty would be shifted so that it is still based around the mechanics of the game (like every other boss before it), yet still pushes you to your very limits due to the level of mastery over it you'd need. For instance, what if regeneration was entirely removed, no matter what potions you've drank, what accessories you wear, or if you have heart lamps or campfires placed, meaning you'd still have to make sure you do not take damage, as you have no possible chance of coming back from a hit without healing. To account for that, the time you have between each time you drink a health potion could be extended, possibly to either the baseline full minute or even over that, so that you cannot bank on it as much as you would have in any other fight before it, forcing you to avoid taking unnecessary damage you can't recover from yet. Damage could be increased even further to assure how drastically each hit of damage is placed on you, defense for the player could be lowered, etc.
There are plenty of things you can do to fix this issue to avoid all of this, and continue to preserve the superboss difficulty Supreme Calamitas boasts, without changing around the base mechanics of the game you've grown accustomed to for the entirety of your playthrough(s).