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.
Rising Mercury, a pounding, insistent orchestral track played in the Maelstrom Valley Dragon Den.
Demonic Spiders: Maelstrom Horsemen. The moment they spot you, they start firing upon you with energy blasts. Then, if you get into melee range, they perform a stun attack that is nigh impossible to dodge. They're also the strongest Stromlings in the game, barring mini-bosses and bosses.
Goddamned Boss: The Crux Prime bosses, sans Roo Morgg, Nuckal, and Butterscorch. Most of them are fairly easy to fight, especially with a team of four players. However, since they spawn randomly and infrequently, good luck finding them. And if you do find them, hope you or your team can get to them before someone else does, or you won't get credit for the kill. And, since they usually spawn amongst many of their fellow Stromlings, it can be frustrating to have nearly defeated one of them only to get killed by some Maelstrom Horseman shooting at you.
Hell Is That Noise: During the battle against the Maelstrom Spider Queen, she shrieks in agony whenever you smash one of her Dark Spiderling offspring.
It's Short, so It Sucks : At launch, discounting property worlds, only six worlds were available, and as far as MMOs go, these worlds are very small. Later worlds, such as Crux Prime, Nexus Tower, and especially Ninjago Monastery, were larger, but much of the game's main story quests can be completed in only a few days, relying on Fake Longevity with tons of grinding to keep people playing.
Narrator: "His foolhardy attempt to control creation through destruction merely created chaos. And creatures of chaos have no master."
The Spider Boss then turns on Baron Typhonus, who realizes its intentions a second too late. He tries to flee from it, but the Spider Boss's foot snags his cape. The last we see of either of them, the Spider Boss is pulling a terrified and struggling Baron Typhonus into the Imagination Nexus, and then the bright blue energy turns purple as it is mutated into the Maelstrom. This is easily one of the Darkest and Edgiest moments in LEGO history, and the background music certainly doesn't help.
During the Spider Queen boss battle, she shrieks in agony whenever you smash one of her Dark Spiderlings.
Upon completing the "Something in the Maelstrom" mission, you are greeted with a vision where your Minifig is sent to what appears to be an elongated staircase in the middle of a Maelstrom vortex. The glowing red image of a skull accompanied by deep Evil Laughter flashes before your eyes as, in the distance, you see a silhouette of Baron Typhonus atop the staircase. Then, tendrils of Maelstrom energy lace out in a double helix around the staircase as the silhouette grows closer and closer. Just before the Maelstrom tendrils slam into your Minifig and Smash to Black, Typhonus towers above you, and you can see that his entire figure is pitch-black, like a silhouette, with his only visible features being the glowing red outline of a skull. This served as confirmation to Master Fong Shader's words: Baron Typhonus is alive, and he is now the Darkitect!
That One Achievement: Many achievements require many, many, many hours of grinding to complete, whether it's completing 11,110 quick builds or smashing 6,150 Stromlings. Needless to say, by the time the game closed a little over a year after launch, most players had not come close to completing these sorts of achievements.
Butterscorch. It has the powerful moveset of most Maelstrom Dragons, plus the ability to spit out numerous fireballs in quick succession to take on multiple players. Nearly all of its attacks have knockback, making it all too easy for Butterscorch to knock players off the small floating island. In addition, Butterscorch has the greatest amount of health out of all enemies in the game and thus takes a lot of time for a team of four players to kill... and if all four players are smashed, Butterscorch regains all lost health. It is easier for a much larger group of players, especially Engineers and anyone with Summon Magic, to quickly take down Butterscorch... but in that case, good luck getting credit for the kill.
According to reports of the unreleased Lord Garmadon boss battle, Garmadon would have also qualified for this trope.
Ninja Tashi and the Ninja Guards are easily mistaken for male. Ninja Tashi at least has feminine eyelashes, but the Ninja Guards have no visible female characteristics unless the player clips the camera through their hoods, revealing their feminine lips.
No one is quite sure whether Shu Fitts is supposed to be female or male. This is due to Shu's hairstyle: is it supposed to be a woman's Tomboyish Ponytail or a man's Samurai Ponytail? Shu's facial features appear more masculine, suggesting that it is supposed to be the latter, though that hasn't stopped many from interpreting it as the former.
There is no way to determine the gender of Maelstrom Dragons such as Butterscorch, though supposedly Bronson Jarls used to refer to Butterscorch with masculine pronouns in an early Crux Prime mission. However, many players mistakenly refer to Butterscorch as a female due to its feminine-sounding name.