Demonic Spiders: Arcane Eyes are flying enemies that harass you with slightly homing projectiles and lasers. They can spot and attack you before you even know they're there, and when you get up close to attack, they can raise their guards and ram you at high speed. Your heavy guard-breaking attack can't be used conveniently in midair, either, so taking them out will involve a skill or careful baiting.
Difficulty Spike: Most notably the final battle, which requires either much higher precision in executing your moves than the rest of the game, or much more upgrades than whatever you likely had by the moment of reaching it, so that you won't be one-shotted by any of the several bosses you will have to fight back-to-back.
Game-Breaker: Tornado Slash turns you into a moving buzzsaw and has invincibility frames for its duration. If you upgrade it, you can extend the attack by holding down your skill button while it slowly consumes more Rage. Hold down the button and down Rage potions regularly and you can just grind away at a boss's health bar without worry of taking damage. This is most effective on ground-based enemies with low mobility.
Archers. They're weak, but they attack at range and up close, and like all enemy attacks they will stagger you and interrupt your combos. They also move very fast (your sprint is only just faster than them), and they have a leaping maneuver that lets them clear a wide distance very quickly... And they often appear in groups of 2 or more.
Wraiths. Unlike other enemies, they continue to spawn even after dispatching them. Touching them causes mild damage and a stagger, and they have a rather large hitbox, making them a supreme nuisance. They also like to spawn in rooms that require a lot of platforming. Worse, they have some of the most pitiful rewards for killing them, being one mana if you're lucky and otherwise just one gold.
Count Santiago cannot be damaged; to advance the fight you have to kill off his numerous minions. While you're doing so he will attack you with homing exploding projectiles and lasers that track you as fast as you can walk — you're expected to be mashing the Dodge button constantly just to traverse the battlefield.
The Devourer is Santiago's second form, and can only be harmed by attacking the jewel on its head. Short of it lowering its head down enough to hit from the ground, you're forced into air combos as your sole offensive strategy while it can catch you off-guard with its attacks and take out large chunks of your health.
Was either of the above enough of a pain to fight? In the Dungeon of the Decayed, you have to fight both of them at once! Even worse, killing all of the Count's minions before finishing off the Devourer will not cause him to die, so you'll have to be constantly dodging lasers as you seek to finish off the latter.
Nightmare Fuel: The last level in the realm of the dead has a lot of frightening imagery.
A lot of the monsters Vivian fights throughout the game, especially the bosses are also terrifying.
"Rune packed" requires you to acquire a piece of equipment with four runestones on it. There are only a few select spots that are even remotely likely to spawn such a piece of equipment, so be prepared for extensive Save Scumming to get it.
"Mana collector" requires you to have accumulated a total of 1,000,000 mana points. Mana accumulation is already pretty slow, even if you try to get as many multipliers as you can to speed up the process. It'll involve more grinding than its currency counterpart, "Wealthy adventurer".
