The Developer's Moat after the Garden filled with deadly Garden Gnomes. There are no enemies and you can't even die here (falling into the moat just ends the level). After that is the true final level with a number of dangerous foes and the Developer himself.
"Yourself" can be considered one if you buy the ability to "overcome yourself" or use a Fire Scroll when his health is low. Before that, you have to literally go through Hell, and after that, you get to face off Chuck Norris.
Demonic Spiders: The Jellyfish in Candy Box 2. Not only do they have a lot of health, they also appear in large groups to gang up on you, leading to Death of a Thousand Cuts. But the worst part is that all of them home in on you, even from behind, meaning that there isno escaping them. If you're planning on getting the sponge and the shell powder early without a good weapon (especially in Hard), you'll have to level scum and hope you encounter the "dangerous fish" (who are much easier to kill and avoid) than these guys.
The peaceful forest and Goblin Mountain are both fairly easy and pretty doable, even if you've been hoarding/spending all your candy. The underwater cavern, however, is much more challenging, and the Castle Entrance will stop you in your tracks if you're not prepared.
The Castle Keep is another one. Lots of painful Mooks, and the Dragon at the end which requires you to have invulnerability potions and a very good strategy if you want to beat it.
Another one occurs after beating the Castle Keep. You end up in hell and fight demons as regular Mooks... who do as much damage as the Dragon, spiked walls that take a long time to break and deal lots of damage, and the Devil himself who does twice as much damage as the dragon.
The sequel has two of them:
Try to go into the desert immediately after you face down the rats, without buying an Iron Axe. You'll get destroyed by the camels.
The forest, after beating the troll. The club you obtain hurts a lot, but it's not enough to face down the huge pack of wolves coming towards you.
Disappointing Last Level: After the Hell level, the game suddenly gets a lot less structured and a lot more gimmicky. Most remaining levels, sans the Luck-Based Mission final level, rely on deriving a single Easy Level Trick to win rather than using a combination of multiple gameplay elements as before. The humor-filled fantasy locations suddenly being replaced by fights with Chuck Norris and an attack on the developer can also cause whiplash for those not too keen on those sort of tropes, though others may find it a neat swerve.
Hilarious in Hindsight: To grind on candies you'll probably be going through Mount Goblin a lot. It becomes a running gag after seeing/reading Goblin Slayer. You'll probably start counting the slain goblins too.
