Items this game desperately needs.

[krugaan]

MacGuffin of Natural Spiritual Balance: When held, this mysterious ... something ... limits the amount of times a creature can be healed by Nature's Spirit to once per cast. Has a range of infinity billion miles.

Scroll of Define Illusion: when read, this scroll describes exactly what shenanigans one may pull off with visual illusions.

Rod of Naming: functions as a mace +1. When you strike the editor for Dnd 5th Edition with this rod, he is placed under a compulsion to review all adventures currently being written and change all terrible sounding names into better ones.

Ladle of Warlock Dipping: This cursed item appears in one of your hands whenever you reach level 2 in warlock. You may not drop or trade this item in any way. It magically disappears upon hitting level 3 in warlock.

Potion of Martial Not-Uselessness: When you drink this potion, you may immediately teleport 5' in any direction. Additionally, while you have at least one of these potions in your possession, whenever you see forcecage being cast, you loudly proclaim that "FORCECAGE SHOULD REQUIRE CONCENTRATION!" as a free action.

[Foxhound438]

spoon of multi-casting-punishment: if a character attempts to cast a levelled spell as a bonus action after casting a levelled spell as an action or vice versa, you can hit the character's player with the spoon, causing the spell to fail

goblet of heals plz: when an attuned cleric is asked for healing mid combat when the player specifically said they aren't a heal bot, they can drink from the goblet on their next turn as a free object interaction to ignore the request and go about their turn however they want

hourglass of minionmancy: if an attuned spellcaster casts conjure animals, they have additional options to bog down combat: 16 beasts of challenge rating 1/8, and 32 beasts of challenge rating 0. Make sure to roll initiative for each beast separately.

Beastmaster's training whistle: an attuned ranger who has the beast master archetype is magically made to not be bad. Use the rules in the Revised Ranger for determining the beast's HP and abilities.

Blood of Sorcerer's Lost Spells: an attuned sorcerer gets to know more spells than the average half caster in this edition

[Twizzly513]

Weapon of the Champion: When wielded, this weapon makes the Champion subclass reasonably balanced to be a viable option for characters.

Lesser Horn of the Champion: As an action you can blow the horn to tell all new players not to play champion for the reason "because it has good crits, dude."

Magical Eraser of Bad Ideas: As an action you can cause the Trickery cleric domain to no longer exist.

Magical Tattoo: This tattoo of a dragon leaps onto your body when you attune to it. It crawls up and down your body periodically. It gives the elemental monk subclass a reasonable amount of options to choose from instead of a few spell-like abilities and convoluted attack patterns that confuse everyone involved and inevitably leads to people getting the book out to decipher for the love of Pelor what it even means.

[Arkhios]

Headband of Crushing Reminder:
Whenever you have cast a spell that requires a concentration and forget to roll it after taking damage, your character is subject to excruciating pain as the band shrinks around your head. You're stunned for one round without a save.

Hempen Scarf a.k.a. Hangman's Noose Tie:
Whenever you start running in circles just to get the maximum possible effect from any spell that restores hit points, you begin to suffocate as the Hempen Scarf appears from nowhere and tightens around your neck. If you attempt the same again, the DM takes control of your character indefinitely.

[Foxhound438]

ah, and one that I forgot:

Prayer beads of **** that makes sense: as an action, you add sunbeam and sunburst to the cleric spell list permanently for all clerics in all universes, because it doesn't make any sense that pelor's own devoted would not be able to harness the power of the sun but some random sorcerer jack*** from the PLANE OF GOD DAM SHADOW CAN

[DarkKnightJin]

ah, and one that I forgot:

Prayer beads of **** that makes sense: as an action, you add sunbeam and sunburst to the cleric spell list permanently for all clerics in all universes, because it doesn't make any sense that pelor's own devoted would not be able to harness the power of the sun but some random sorcerer jack*** from the PLANE OF GOD DAM SHADOW CAN

Wait.. Clerics don't have Sunbeam and Sunburst on their spell list by default?
Guess I need to sharpie some additions to my PHB..

[krugaan]

Headband of Crushing Reminder:
Whenever you have cast a spell that requires a concentration and forget to roll it after taking damage, your character is subject to excruciating pain as the band shrinks around your head. You're stunned for one round without a save.

Damn, man, that's harsh, roflmao.

[Glorthindel]

The Rapier of Clumsiness +1 - all other Rapiers in the world lose the finesse trait. The +2 versions causes all Shortswords in the world to lose the finesse trait too.

The Jealous Spear - all spears within 100 miles are counted as Polearms, and all quarterstaffs within 100 miles are not.

The Dark Runesword of the Munchkin - curses all multiclass characters with a level in Hexblade lower than their level in another class to use Strength for combat. If such characters have only a single level in Hexblade they are forced to use their lowest stat for combat.