Ankh Shield

Knockback immunity is the part you notice first: no more being punted off your own bridge mid fight and no interruption in the middle of a jump. Of the debuffs it blocks, the ones that matter in practice are Silenced and Cursed, which stop you attacking at all, and Broken Armor, which quietly doubles what you take. Where it lets you down is the upgraded versions. It does nothing against On Fire, Cursed Inferno, Ichor, Acid Venom, Frozen or Blackout, and those are the ones you meet in the fights where you wanted help.

None of the components come from a Hardmode boss, so the shield can be finished before you break the first mechanical one. Four of the base accessories can even be found before Hardmode at all, which is worth knowing while you are still working through the Underworld and the Jungle. Everything else comes from ordinary Hardmode enemies, and the drop rates are the entire difficulty. One component, the Obsidian Skull, is the only crafted piece in the chain that is not made at a Tinkerer's Workshop.

Each base immunity accessory transmutes into its partner, so you can farm whichever side of a pair is easier and convert. Collect a spare Blindfold rather than hunting Medusa for a Pocket Mirror. Take Armor Polish off Armored Skeletons instead of walking into an evil biome for Vitamins. Pixies hand out Megaphone drops constantly, so convert one instead of grinding for a Nazar, and pick up a Fast Clock while you are there. A Bezoar can be farmed before Hardmode even starts, which spares you the Adhesive Bandage hunt that otherwise waits on full moons and angler fish.

Equipping it clears debuffs that are already on you, so it does not have to live in your loadout permanently. Park it in a spare loadout or even a vanity slot and switch over the moment something lands. The debuff comes off immediately and you switch back to whatever you would rather be wearing, which gets you the utility without paying an accessory slot for the whole fight.

For boss fights on their own the Paladin's Shield is generally better, and its Frozen Shield upgrade adds flat damage reduction that no immunity list can match. The Ankh keeps its place in the fights that spam status effects, which in practice means Duke Fishron on the higher difficulties and the Frost Moon. Against Fishron it is a strange bargain: it blocks everything Feral Bite inflicts while leaving you the damage bonus that same bite grants. It also counts as a shield for the Brand of the Inferno, so you can block with it and pick up the buff that follows a successful block.