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.
YMMV: Ginormo Sword
Anticlimax Boss: The Avatar, but only if you have the Hyper Armor and a highly Dark-enchanted sword. With the Hyper Armor, ALL his attacks will only deal Scratch Damage, and a strong Dark enchanted sword will help you deal damage faster than you receive. Without the Hyper Armor, he's very tough.
Demons appear in up to threes and use the Vampire's Spread Shot and the Maze Minotaur's bullet spiral, and they have much more health than Liches, Vampires and Succubi.
Fridge Logic: The Sand Golem is not a part of the Golem family of enemies, but a species on its own. Maybe because he's so weak.
Game Breaker: In several areas, you fight all types of monsters (often nearly every non-boss type you've encountered so far), and all of them give money on par with monsters that belong in that section of the map. In the last of these areas, even the weakest of monsters give out five digit payoffs.
If you're lucky (Or unlucky, depending on your point of view) when going through that area, you can find Ambrosia, the strongest member of the Gargoyle family. Taking it down will take you an eternity, but the reward for doing so is so high your eyes will go wide in awe.
Most Annoying Sound: the sound of your ally finally getting around to healing you... when you're already dead.
Scrappy Mechanic: Counter hits. If you get hit by a projectile while swinging your weapon, you take a lot more damage, potentially suffering a One-Hit Kill. You are always swinging your weapon. One of the best accessories is the one that turns this mechanic off.
That One Attack: The Guardian Dragon has three attacks. The first is a Spread Shot of fireballs, and the second is a Breath Weapon fired in front of it. Both of these are very easy to avoid if you stand in the right position. The third one is a spiral of fireballs (like the Minotaur and Efreet) that also leaves explosions in their wake, which is tricky to avoid and deals a hell lot of damage.
The Sorceress also has three attacks. The first is a Spread Shot of whirlpools, avoidable if you're far and squeeze in-between the gaps, the second is a slew of aimed fireballs, which is avoidable if you keep moving. The third is a lightning attack that aims at you and comes out extremely quickly, and can probably one-shot you when you first face her.