These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
The Narukami Bracelet/Thunderous Bangle also prevents any Soul Power loss from using special attacks, only it lasts forever. Since you get it for beating Total Pandemonium, it's almost a Bragging Rights Reward, except the game is skills-based, and you can never become so powerful that the game becomes a walk in the park.
There's also the Nio bracelet you get from the dragon god in the post game of Momohime's story. This item makes the attack of all swords 700, which becomes brutal when comboed with something like Gale II. Only 3 swords are made worse by this item, and you don't get them until you start getting the 3rd endings.
Goddamn Bats: Pheasants and poison moths. Tengu can also be pretty annoying, since they usually show up in areas with differing elavation, which makes chasing them down or avoiding their attacks a pain.
Kite ninjas as well, as they love to fly just out of reach while pelting you with shuriken and bomb, and have a nasty habit of blowing up in your face when they die.
MST3K Mantra: During the reign of Shogun Tsunayoshi Tokugawa, it was illegal to be a prostitute, sell silk, hire waitresses in your restaurant, or hurt animals. The game pretty much only paid attention to the "hurt animals" part. Justified in as much as these things are part of the Jidai Geki feeling it is attempting to emulate, and their loss would make for a poorer game.
Nightmare Fuel: Some of the bosses are truly awful-looking. Especially the giant centipede. *shudder*
Inugami is disturbing as hell.
Polished Port: The Vita version adds a lot of improvements over the original Wii version. Aside from DLC characters and even prettier HD graphics, the presence of an actual jump button instead of the awkward up button to jump improves the gameplay immensely. The localization was also handled by Aksys (the same localization team of the BlazBlue series), with an eye toward a more faithful translation than Ignition's widely disliked version.
Scrappy Mechanic: Enemy scaling rears its ugly head. You can be fifty levels above the recommended minimum for a lair, with thousands more HP and ten times more attack power than you're 'supposed' to have, but they still hit hard and soak up the punishment you deal out. So fighting random battles doesn't do you much good... but you have to level up because there are minimum stat levels on the swords.
Ugly Cute: Ippondatara's boar form. When you're fighting him he just seems like some regular monster, but then you beat him and he asks you to spare his life in exchange for information. Gets even more cute when he explains that he transforms into the giant monster you fought, because he wants to protect his hot spring from humans. He tells you this while bathing in the hot spring himself with Momohime and Kongiku.