Sergeant United Shield

Nothing drops it and there is no recipe. It appears in the Traveling Merchant stock and only rarely, so getting one means checking him every visit and keeping the gold on hand for the day it shows. The boomerang half is ordinary. The parry attached to it is the reason to keep looking.

Thrown, it seeks out enemies by itself and bounces between a handful of them before returning, giving up a slice of its damage at every stop, so the last target in a chain barely feels it. Worms are the exception: it treats each segment as its own body and works down the length of one happily. It also flies out and back faster than you can throw it again, so most of the cycle is spent waiting.

Hold it with any shield accessory equipped, including this one while it is in your hand rather than in the air, and the activate key becomes a parry. Tap it just before something reaches you. Land the timing and the contact damage is refused outright, the attacker takes a heavy hit back and gets shoved away, and you get a stretch of invincibility to reposition in. Miss and you have simply flashed a shield, which costs nothing but the moment. A brief cooldown follows each attempt, and the game announces the reset with a small sparkle and the chime you hear when mana refills, so the rhythm is learnable by ear.

Every successful parry hands you a short buff that multiplies your next melee hit enormously. Spending it on this weapon wastes it. The intended play is to parry, swap to the heaviest single hit you own, and connect once before the window closes. Psycho Knife is the usual partner because its stealth bonus stacks on top, and the combined swing produces one of the largest numbers in the game. A Cross Necklace doubles the invincibility a parry gives you, which is what makes that swap comfortable instead of frantic.

• Only contact damage can be parried, and the enemy has to actually collide with the shield before it reaches you. Projectiles, traps, lava and falls go through untouched.
• Holding the key instead of tapping it is a different move: you plant yourself for a large defense boost and lose most of your movement speed until you lower it. Useful for eating an unavoidable moment, not for fighting.
• The damage you reflect is capped, and banners for that enemy cut it further, more so in Expert and above. Treat the reflected hit as a bonus and the buff as the real reward.
• Godly and Demonic come out even here, so take whichever you roll first.

It parries things that normally ignore every other defensive trick, the Dungeon Guardian included, which makes it one of the few honest answers to walking into the dungeon too early.