Natsu becoming Drunk on the Dark Side with Ignia's power, as he enters a berserker rage, with pupil-less eyes, and unrestrained destruction, making seem all too similar to E.N.D.. Lucy even lampshades how it's the first time Natsu's flames actually scared her.
Seeing all the members of Fairy Tail (sans Team Natsu) "turned white" by the White Mage, and being brainwashed into being her servants. The White Mage even forces Elfman and Lisanna to brutally pummel Mirajane just to demonstrate her control over them.
The White Mage undergoes major Body Horror when Happy chucks one of Aldoron's orbs at her back, causing her to mutate uncontrollably and temporarily gain branches all over her body.
Diabolos is a guild of fifth generation Dragon Slayers (they ate pieces of dragons to get their abilities). They do not suffer from motion sickness, but they do have one glaring taboo: they must never use Dragon Force. Nebaru breaks this restraint and undergoes a rapid, irreversible transformation into a feral dragon. After he loses what little sanity he possessed before he transformed, Diabolos leaves him for dead, indicating there's nothing they can do to recover their guildmate.
After Selene captures Team Natsu, she forces Natsu and Gray to fight their way through the lower reaches of her mountain, which is filled with yokai they have to fight. The caveat? Amongst those yokai are their remaining friends, all transformed into monsters.
The new forms they possess are deeply unsettling in of themselves. As a nure-onna, Lucy's lower body is turned into that of a snake, with scales on her shoulders and back, and cold, reptilian eyes; Wendy (transformed into a bakeneko), while otherwise cute as a Cat Girl, also acquires cold, cat eyes; Happy and Carla are both transformed into suiko, and the otherwise cute Exceeds become massive, savage looking, tiger-like cats. Erza's form is possibly the worst: she becomes a jorougumo, where her entire lower body becomes a massive spider complete with a fanged, gaping maw.
On top of the physical changes, their personalities are also completely changed, and their identities are stripped away from them. The otherwise pure and kind Lucy is turned into a violent and manipulative predator, the sweet and innocent Wendy becomes sadistic and cruel, and Happy and Carla are reduced to savage beasts, with all of them gleefully expressing their eagerness to hurt Natsu and Gray respectively.
After being cruelly manipulated by the transformed Lucy, Natsu gets very angry and was about to use Lighting Flame Dragon Mode to outright kill her (possibly thinking the Lucy he knows is now dead inside and he's facing a shadow of her former self who is beyond saving). Thankfully, Aquarius makes her entrance and defuses the whole thing.
Alta Face, who brings back the terrifying design of the Face weapons from the Tartaros Arc and is one of the beings responsible for the magical chaos and distortion in Elentir, along with Selene herself. It's also tough enough to tank the entire main cast's attacks like nobody's business.
Gottfried is shown once again to be horrendously powerful, and it's lucky that Lucy managed to find a way around harming herself using the spell... as Kiria is the target of the spell, however, she is not nearly so lucky. We last see her lying motionless on the ground, completely naked and burnt to a crisp with Blank White Eyes and smoke pouring out from her open mouth and several other particularly tender body parts. Essentially, she resembles a charred corpse. She'll be lucky to wake up, let alone fight ever again after that finishing move. Also counts as a Crowning Moment of Awesome for Lucy after everything she had been put through. Mitigated later in that when Kiria shows up to help smash the orbs she looks fine if a bit scuffed up.
Selene and Ignia are about to clash, and the devastation will undoubtedly be a sight to remember. One can't help but worry over who may be killed in the crossfire...
When Fairy Tail and Sabertooth travel to Filan, Lucy and Happy run into a very creepy old hag who has sunken in eyes with dark sclerae, missing teeth, wrinkled lips, and a nasal cavity in place of a nose. She looks just like a withered mummy. Later, it's clarified that she was one of many artificial lifeforms made to resemble humans by Viernes, and her ghastly appearance was most likely intentional.
