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: Azure Dreams
Complete Monster: Beldo initially traveled with the father of Kid Hero Koh, Guy in order to find the Ultimate Egg to give him ultimate power and Take Over the World. Beldo betrayed and killed Guy and later killed the father of Koh's rival as well. Beldo mind controlled Koh's partner Kewne, against Kewne's will, to lead Koh to him to unseal the Ultimate Egg, and after killing Guy, he forcibly transformed Guy's partner into a new right arm to replace the one guy chopped off against said partner's will. He proceeds to use Guy's sword on Koh to use Koh's blood to unseal the Egg, mocking him all the while. He even fuses monsters to him against their will in his quest for power.
Contested Sequel: Tao's Adventure: Curse of the Demon Seal is considered this, although it doesn't seem to be a true sequel, what with the absence of Koh or any of the other characters. It tried to implement a character could use magic, along with different monsters, and a setting that was very similar to the first one, with the Monster Tower still being the main focus. The main faults however, are that the game is much easier, being able to leave the tower whenever possible, no monsters that reappear from Azure Dreams (including a main familiar that wasn't even too useful like Kewne), an annoying spell system, being able to move up and down the tower with no consequences, no randomized floors, and more. There are a few fans that like it for the similar gameplay, but the sequel itself is generally very unliked.
The closest thing that the game had to the original, along with the Monster Tower snd items found in it, was a man with the last name Rhode. It's unknown how he is related to Ghosh and Selfi.
Demonic Spiders: Arachnes to a literal extent. Also, most monsters have special abilities unique to their species. Some of them are more annoying than others. If a monster isn't this, it's probably one of a horde of Goddamned Bats.
Balloons can ship you up to the next level, which can be especially bad if you're looking for an item on a specific level.
Blooms, who are not that big of a threat themselves, have a tendency to brainwash your monsters with their special ability. Kewne is the only monster who can't be mind-controlled due to its ability Unbrainwashable, and it doesn't seem to matter what level other monsters are to have them brainwashed. Once brainwashed, your monsters won't obey commands, and instead attack you.
Krakens, who have the ability to deliver massive electric recoil whenever you strike it directly with a metal weapon. This forces you to use only weak wooden weapons to fight them, or find a Barong and throw random items into its mouth and hope it gives you a Trained Wand which is a wand that can be powered up by sand like a sword, but has the same affect as the wooden wand and wouldn't allow the Krakens to deliver recoil.
Killers have high attack stats, and an even higher critical hit ratio, and they love to come in multiples.
Pickets have the ability to steal an item, which was usually pretty important, and they can teleport and move twice as fast as you.
Submars (U-Boats) can make themselves unhittable by sinking into the ground, and sneak under your monster to attack Koh directly.
Vipers can eat eggs in the area, forcing you to defeat it to get the egg back. They can also continuously lower your attack every time the hit you.
Weadogs can throw meat which will distract your familiar into eating it, while you have to fight alone until they finish eating.
Additionally, a large variety of common monsters throughout the tower love to inflict Poison, Confuse, Sleep or Paralyze on your monsters.
Faux Symbolism: The necklace that Guy gave her breaks the very second that he dies.
Fridge Brilliance: Kewne has the ability Unbrainwashable. Later in the story, when you get to the top and meet Beldo, he's forced to comply with his master. When Beldo is about to kill Koh, Kewne separates from him, showing that he was never really under Beldo's control, just waiting for a moment there would be someone to take him out!
In the beginning, you see a cutscene involving a massive circle of light with a star in the middle that spins at the top of the tower and shrinks, no one completely certain of what they saw. In the tower, two of the magic Traps is the exact circle with the star inside, with one transforming those who step onto it into a frog, and the other sealing magic. When you get to the top floor, it is revealed that Guy summoned the massive star circle himself so that Beldo wouldn't be able to obtain the Ultimate Egg. It was by a similar magic that he SEALED it.
Fridge Logic: While it's true Koh wanted to go into the tower partially because he wanted to find out the fate of his father, what if he never went up to the top floor? Considering most people seem to only make it to the first few floors, would he be stuck there forever?
At one point, Selfi is being attacked by a Pulunpa, but it looks like its... doing something else to her. Later on, she gives you a Pulunpa Egg...
Game Breaker: The ultimate monster can make your weapon instantly kill all enemies in a 3x3 box in front of you, and he also has a spell that makes you invincible.
Way before you get to that point, fusing a Block and an Arachne together will create a double-attack Block that could kill anything but the final boss and take only 1 point of damage. An unkillable monster that one shots everything is as useful as it sounds.
While it's pricy, buying a Casino and learning how to play the games means that you have an unlimited supply of money, removing the need to collect items in the tower to sell and simply allowing you to buy everything.
Your safe increases the chance of an item dropping by the number of the item you have stored. A Barong could swallow any item you throw at it and spit out a random one. These two in combination would allow you to get whatever item that you would want.
Moe: Cherrl definitely fits this. She's one of the cuter girlfriends whose Ill Girl trait makes you want to see her healed all the more, with an innocent desire to be able to leave her home and help others. Her feelings for Koh are also very immense, hoping that she marries him, even if it means she gets sick again. This definitely allowed her to become a favorite of players.
All of the love interests, to a greater or lesser degree.
Nightmare Fuel: The entry for the Clown shows it holding the head of a decapitated Nyuel.
Killers also qualify, especially when you realize the damage they are capable of.
Ridiculously Cute Critter: Pulunpas(PS1)/Catawumps(GBC). Also Wumps(baby Catawumps), especially Wumpi, Selfi's familiar that helps show her kinder side.
The Scrappy: Noise are considered to be the worst monsters in the game, even lower than Pulunpas, due to their abysmal stats, and the fact they are only on the first floor of the tower. Pulunpas on the other hand are seen throughout the tower, even having a few later on that can steal your collars, and are also considered a Ridiculously Cute Critter.
Self-Imposed Challenge: Seeing how far you can go up the tower by going in with nothing, only using the items you pick up in it.
That One Monster: Krakens, who have the ability to deliver massive electric recoil whenever you strike it directly with a metal weapon. This forces you to use only weak wooden weapons to fight them, or find a Barong and throw random items into its mouth and hope it gives you a Trained Wand which is a wand that can be powered up by sand like a sword, but has the same affect as the wooden wand and wouldn't allow the Krakens to deliver recoil.
That One Sidequest: Finding the Healing Herb for Cherrl, mainly because it's on a high floor and it looks like any other plant, so you won't know what it is until you pick it up directly.