Gamebreaking items.
 

If you had a fungi tunic, you could literally get any class that can wear it to lvl 45 solo on autopilot just grinding through mob after mob...

You could wear just that single shirt and still get to lvl 45, fifteen times faster. I can't think of any other item in the game so powerful and trivialize so much content. Maybe a manastone?

Are there any other items that have such a huge impact on the game?

not really

+15hp a tick doesn't make you kill mobs 15x faster. Better than a sharp stick in the eye tho

here's a tip: you can click jboots to go faster

Not really. Fungi is broken. Only other item I think that alters the game so much would be OT hammer. Hard to imagine the game if melee couldn't teleport whenever they wanted.

I remember when archery was broken and had 0 delay for like a day and a half. That shit was fun. But yeah, OP'est item would be fungi I think. Manastones not even close.

On that note, I'd probably have to say Leatherfoot Raider Skullcap, which has saved me from innumerable deaths and painful CRs at the fairly low cost of ~180 platinum per use. I rarely go anywhere without having it charged.

Midnight mallet, wort pots, bladestopper, prayers, soulfire, reaper...

Raid and aggro management trivialization no doubt.

Of course while not being an item, recharging is one of the most game breaking and immersion shattering things on p99. Classic, but not widespread knowledge.

And yes, fungi should have been a no drop item in VP, no business being tradeable from seb camp.

Anything that clicks for free dmg especially dots (shm epic, druid epic) I don't have a necro or ever clicked a necro epic so don't know for sure on it

To me feels hella broken can kill anything that doesn't summon for basically free with these epics for just root and time waiting for the clicks to work.

Necro VP staves are pretty unreal once you get one. Infinite health, Mana, and free damage. It's a shaman epic that steals hp. Bonkers good solo