Crosses the Line Twice: Some of the death animations; The Many Deaths of You is nothing new for the Adventure Game genre, but most adventure game protagonists aren't about five years old when they get impaled on giant bee stingers or eaten by monsters.
Chronicles of Teddy
Awesome Music: The game has some fantastic music (available as a DLC), perhaps most memorably 'Books', the gorgeous theme of the Library.
The Electric Slimes from the Neika Mountains; even though they still die in one hit, they have an irritating habit of channeling electricity through themselves when you go in to attack them, making them invincible and hurting you if you strike them. They can hold the charge for a lot longer than you might expect, leaving you sitting there waiting patiently ages for them to stop so you can hit them, and a lot of the time the instant they stop they'll jump right at you, possibly catching you off-guard- and then starting up their electric attack again, in mid-air! If they weren't so easy to simply ignore and jump over they might even border on Demonic Spiders, so rage-inducing is their pattern.
Enemies that explode on death — which in the Monster Valley, is almost all of them. Acid Slimes in particular combine this with the electrical defense mentioned above, as well as periodically hurling burning projectiles if left alone.
Fire Slimes, in addition to exploding on death, leave a trail of fire every time they move. With your incredibly short attack range, it's very difficult to hit them without getting hurt.
Fire Orbs. They're aerial enemies that float in a sine pattern, similar to Castlevania's Goddamn Bats, the Medusa Heads. The upward and downward thrust attacks can defeat them fairly easily... provided they're within jumping height. Many of them float well above your range, requiring a tricky Double Jump to reach, if you can reach them at all. The upgraded version introduced in later areas periodically drops fireballs, which may well push them into Demonic Spiders territory.
Your absurdly-short sword gives you a depressingly limited attack range which requires extreme precision to let you hit opponents without getting hit in return, a matter not helped by the somewhat slippery movement.
The fact that as well as a dedicated run button, the game also makes you run by double-tapping in a direction. While a common enough control setting in platform games, it tends to trigger unintentionally if you move forward, take a small step back, then try to step forward again (something you'll want to do when trying to duel certain enemies in close quarters), sending you crashing headfirst into them.
You can't attack during the Double Jump animation, which will likely throw off your timing and shove you straight into enemies you were trying to attack. This makes it very difficult to attack enemies that fly above the range of your regular jump.
That One Boss: Harao, for the reasons listed under Wake-Up Call Boss on the main page; it's very hard to stun it, and even if you do, you have to be really quick to damage it and get away, because if it runs over you it will hurt.
, the gorgeous theme of the Library.