This was further complicated with the revised poem being a Take That from the user to the people who complained, which only led to more arguments in the fanbase. It's worth noting that right now, one of the more popular mods in the game is bringing the original limerick back.
Demonic Spiders: Shadows, made worst by the fact that they show up early in the game. They deal a surprising amount of endurance damage, have a chance to stun on hit, and, perhaps most annoyingly, love to ignore your frontline fighters in favor of teleporting right to your squishier long range characters.
Fampyrs, who spam Charm willy-nilly as soon as combat begins. Any fight involving them (especially if there's more than one) devolves into a chaotic mess, as half your carefully selected and placed group begins attacking the other half.
Perhaps surprisingly, the Mercenary Brawlers and Drunken Orlans in the Cragholdt Bluffs can be some of the toughest enemies in the game, thanks to a combination of their ability to duplicate tehmselves, other mobs in the area supporting them (such as mercs with ranged weapon stun abilities), and having the ability to teleport, which they use to attack your squishiest party members.
The Cipher's Mental Binding spell. It's a paralysis spell that's fast, fairly cheap for a Cipher spell, and most importantly, available by third level. This is thee absolutely earliest one can inflict paralysis, allowing Ciphers to shut down plenty of enemies right from the start. Considering one can be only a few hundred experience short of level three before they even reach Gilded Vale...
Some combinations of spells can quickly lead to the demise of your enemies. The Wizard in particular has Chill Fog which deals Freeze damage but, more importantly, blind your targets (which reduce their Accurancy and Deflection by a whooping 25 and 20 respectively!), Expose Vulnerabilities, which lower damage reduction, deflection and concentration of your foes (and there is no risk of friendly fire while using it) and Call to Slumber, which make characters prone, preventing them from taking any actions and reducing once again their deflection.
The almighty Devotions of the Faithful priest spell, which not only dramatically increase your character's accuracy (+20 for both melee and ranged), but also decreases your enemy's accuracy by the same amount, while improving your Might by 4 and decreasing your enemy's Might by 10. This one spell can absolutly cripple your opponent while buffing significantly your allies.
Gaze of Adragan, a 6th level wizard spell, can petrify multiples foes. It comes pretty late, but once you can cast it, every single encounter of the game becomes a joke if your targets are petrified, since not only are they stunned, but they also completly lose their damage reduction, and the effect lasts for 20 very long seconds (and since Wizards usually have high Intelligence, your foes can be petrified for over 30 seconds quite easily, leaving you ample time to kill them). Scrolls of Petrification have a similar effect and can be crafted from relatively common ingredients.
Also the Cipher spell Amplified Wave. It's a level 6 spell, so you'll get it only very late but boy is it ever powerful. It's targeted on a friendly and inflicts an enormous foe-only Ao E, dealing a substantial amount of crush damage and knocking prone. Encounters that would have been challenging like Banshees and Shades become an absolute joke as they'll be knocked down for basically the whole time. And this being a Cipher spell you can cast it every encounter multiple times if you wish, there's no limit on daily usage.
Genius Bonus: This game is basically Thus Spake Zarathustra: the game. The overarching plot is that the ancient Engwithans used animancy to create the "gods" so that folk would have something to believe in that would give their lives order and meaning. They also used animancy to grant a form of immortality to Thaos so that he could make sure that the lie would never be uncovered. Iovara, however, discovered the secret and tried to reveal it to the world, believing that people would still be good, and that life would still have meaning, even if the truth were exposed. This was, in essence, Nietzsche's view of religion: a handful of ancient visionary heroes had created religion to give humanity something to believe in that would give our lives order and meaning. Without that, humanity would slowly go extinct unless a new visionary hero could somehow create values that people would live and die for without any belief in a higher power.
The Orlans are like a sort of hybrid between hobbits and cat people, and have been constantly enslaved and victimized by all the larger kith races, to the point that they've been driven further into the wild or resorted to guerrilla warfare. This is as likely as not inspired by an interview by Tolkien, where he denied The Lord of the Rings being a direct allegory to WWII because, among other reasons, both the humans on Aragorn's side and Sauron's side would have enslaved the hobbits since they were so small and easily dominated.
The Chanter class is basically The Bard, but powered by necromancy; chanting stirs whatever ghosts are nearby to aid the Chanter's allies and hinder their enemies. While they still have the popular Summon Magic trope, as a whole the class is much closer to mythological necromancers than the classic goth-flavored Mook Maker. Bonus points if you make your Watcher a Chanter, for the full suite of white and black necromancy.
He's Just Hiding: The game makes it clear that Eothas was nuked and destroyed. Indeed, he is the only god you can't speak with during act 3 and 4; even the ones who refuse you at Teir Evron, Wael and Woedica, prove themselves quite alive at other times. Many believe that he somehow survived, that he is bidding his time, or that his resurrection just takes a while. Some little details also reinforce the possibility that he is not quite dead, since the candles in his temple never stopped burning and he is actually the second god to be killed while in Eora, and Abydon did come back eventually (if somewhat diminished). Also, the Watcher can be a priest of Eothas, and still cast spells; while spells are explicitly cast from intense belief in a god's philosophies rather than directly derived from gods, it's ambiguous whether or not it's possible to be a priest without any god to at least provide the "spark".
That One Attack: Charm and Dominate spells are vicious, especially considering how common they are in the late game.
That One Level: Related to the Demonic Spiders entry, the Temple of Eothas in Gilded Vale can be this, depending on how early in the game you take it on—its second level is absolutely filled with Shadows. Still, this can be mitigated by building up a full party, or a bit of leveling and returning later.
The Wailing Banshee lighthouse is especially brutal compared to the other dungeons in the second act, as it too is filled with Shadows and Shades. Thankfully the level is optional and any player can avoid fighting the nightmarishly-hard Banshee on the top floor through non-lethal means.