Any item but cursed with wild magic, if you swing that sword, roll the d100 of wild magic.
Cursed ring of acrobatics.
Gives the player great acrobatic skill, but sticks to their finger when they wear it. And they can't stop getting around acrobatically. Any action attempted fails, unless it is done acrobatically. Player has normal or only slightly improved stamina.
Player: i'll get my rope and grappleing hook and scale the wall.
DM: lifts eyebrow you think so, do you?
Player: sigh I throw my pack into the air and leap after it. At the peak of its arc, I flip over it, grabbing my grappling hook and flinging it over the wall as I do.
DM: ok, sounds like difficulty of 15..
Ring of perception filter, when not visible (or mentioned recently) creatures forget it exists
Cursed variant applies this effect to the wearer
Alchemy Jug
Source: Dungeon Master's Guide
Wondrous item, uncommon
This ceramic jug appears to be able to hold a gallon of liquid and weighs 12 pounds whether full or empty. Sloshing sounds can be heard from within the jug when it is shaken, even if the jug is empty.
You can use an action and name one liquid from the table below to cause the jug to produce the chosen liquid. Afterward, you can uncork the jug as an action and pour that liquid out, up to 2 gallons per minute. The maximum amount of liquid the jug can produce depends on the liquid you named.
Once the jug starts producing a liquid, it can't produce a different one, or more of one that has reached its maximum, until the next dawn. Liquid Max Amount Acid 8 ounces Basic poison 1/2 ounce Beer 4 gallons Honey 1 gallon Mayonnaise 2 gallons Oil 1 quart Vinegar 2 gallons Water, fresh 8 gallons Water, salt 12 gallons Wine 1 gallon
Hammer of Dwarf Throwing.
Can only be attuned to by dwarves. As a bonus action, the user may expend a charge to be launched from the location of the hammer towards a target, leaving the hammer behind.
In one of my dungeons, there was a trapped carpet which caused people who sat on it to belive they were riding a flying carpet. It was in fact an animated carpet, so the barbarian who believed he was flying around the castle was in fact just scooting forward an inch at a time
One I made up for a caster who always missed their rolls was a sentient wizards had 'clippy'. "I see you were trying to cast Eldrich Blast, do you need help with that" and occasionally giving them advantage (they really were rolling awfully)
I was bad at RPing it though and that campaign ended shortly after anyway
This isn't exactly what you were asking for, but thought I would share a funny story from a few years ago.
I had a problem player, fell asleep during games, made other players uncomfortable with unwanted advances, would say racist things in and sometimes out of character, etc. So I decided to have a bit of fun on what I knew was going to be his last session with our group. He had wanted a ring of invisibility or a powerful magical crossbow. I gave him both.
The ring was not the kind you wear on a finger though, and he had to spend a full minute to put it on as it required some.... prep, he was so embarrassed he never even tried to use it.
The Crossbow was hot pink, covered in glitter, and became soul bound as soon as he attuned to it which was as soon as he picked it up. It shot 4 Eldritch Blasts per attack action, and gave a free attack action every turn. It also compelled anyone within 100ft of the bow to refer to the wielder as Sparkle Bitch. Small price to pay, so he thought. Problem is, the Crossbow was a cursed item and after the wielder fired 20 shots, all the damage it dealt would be added up, multiplied by 10 and then dealt back to the wielder in an explosive cloud of pink glitter. I don't recall the total, but was easily 4 times the players max HP. He was pissed, and that's when I told him he was no longer welcome at my table.
More in line with your request though: A magical whistle, when you blow it, once per day you can summon an army of 1D6 chickens who will then follow you around until your next long rest. You can have the army attack dealing 1D4 damage multiplied by the number of chickens. The chickens are unkillable, and vanish in a cloud of feathers when you take your next long rest.
In my last game one of my players got a seemingly dubious treasure - an apron. He later found out it was The Apron of Deliciousness (based on Delicious in Dungeon). He could make monsters and other seemingly non-food items into delicious meals. At one point while trapped in a cave he kept everyone alive with spiderweb soup. queue the horn sound
A funny one i found on Reddit:
Glasses of hindsight: provide a passive perception of 20 of events suitably far in the past
Be careful with magic items, I let my guys buy a trident of fish command.... In a desert. But it turns out lots of snakes etc have a swim speed....
It works on a beast with swim speed (doesn't need to be a fish)
https://www.dndbeyond.com/magic-items/4784-trident-of-fish-command
We had one that was a jar of peanut butter you couldn't give away or get rid of bc it'd teleport back immediately. It also gave a huge migraine and did damage if you ate it, and it refilled daily
