Seeing how the list is pretty much almost done, I went back through and came up with a few more suggestions to help finish up.
-Flying Carpet: B -> A
The Flying Carpet is a lot more useful than people like to give it credit for, probably because it’s competing with the Sandstorm. However for the stage of the game you get it at, it’s probably one of the more useful accessories: fast(er) world travel, the ability to glide over enemies or threats, more reliable fall damage blocking than any alternatives.
-Fart in a Jar: S -> A /or/ Sandstorm in a Bottle: A -> S
Giving it the same treatment as Sandstorm, it’s a bit too rare to be practical. Yeah you technically get the Fart eventually, but have you ever tried actually farming worms early game? It’s more practical to just... find a damn Blizzard. Either it should be cut down to A, or Sandstorm brought up to S (preferably the second, as Fart and Sandstorm have a pretty big advantage over the other bottles).
-Jellyfish Necklace: F -> D
It’s not good, but it’s not completely useless. 1.4.1 made it emit an (admittedly small) amount of light, so if you chance upon it early enough you can use it to make your life marginally easier in caves without wasting a helmet slot. It can also help explore the oceans and any ocean tunnels, however small a niche that may be.
-Sweetheart Necklace D -> C
Panic and Honeycomb are C, which is reasonable for their strength, and it’s not any harder to make the sweetheart necklace than the honeycomb considering that the panic necklace is incredibly easy to get.
-Philosopher’s Stone/Charm of Myths: AB -> S
I think I said this already, and I don’t know if it counts, but these are literally free to use on singleplayer, resulting in 25% less potion cooldown basically whenever. Just make sure you have Autopause on before bosses.
-Frozen Shield A -> S
I stand by the opinion that this is the only knockback immunity item worth S tier. This is the point of the game where knockback becomes more important, as you need swift and uninterrupted movement during this stage, and the Frozen Turtle Shell effect is so powerful on its own that it gives a massive boost to how good the shield is.
-Diving Helmet and all further tinkers: CB -> F
Unlike Jellyfish Necklace which you can get sometimes by being in a cave, these require you to venture over to the ocean and farm out potentially hundreds of what is one of the strongest enemies stat-wise in prehardmode. And it became even harder after 1.4 reworked water enemy AI, which made it take up to 15 minutes to just get the five Shark Fins you need for Megashark, let alone farm for an item that has a **2%** drop from them. Its not even a good accessory, and it’s so goddamn rare and so easily replaceable by so many things that you should *never* try to farm it out.
-Leaf Wings B -> A
Yeah, they were nerfed. But they have the advantage over Angel and Demon of being basically free, while Angel and Demon require somewhag of an undertaking to get in the first place. It’ll hold you over until Pixie, Harpy or Frozen at least.
-Flesh Knuckles B -> C
Compared to Putrid Scent, this doesn’t do nearly enough to be worth using in singleplayer. 8 defense is not that much, being 4 less damage in Normal and 8 less damage in the mode you’re taking triple the damage of Normal. And unlike aggro reduction, aggro expansion does basically nothing in singleplayer except *maybe* help distract Old One’s Army enemies, but it’s less effort to just stand by the crystal and kill enemies as they approach and delve into offense.
-Greedy Ring A -> B/C
Considering how an accessory's rarity is a major player into its tier, as evident by Sandstorm and Terraspark being A among others, this definitely deserves a cut for rarity. Its components are good enough for A and B rank when you get them, but getting all three of them for Greedy Ring is possibly even harder than getting the Coin Gun. And its components are niche enough to where you’re probably using them for separate things anyway, so you shouldn’t need to combine them into one. I just don’t know if it’d be B or C.
I think that’s all I want to critique. Great list overall, love how it turned out.