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.
Breather Boss: Let's put this simply, in Monster Rancher the difference between fighting a Fragile Speedster, Glass Cannon, and a Mighty Glacier is the fact that against the speedster and the cannon, you need tons of luck to hit them, but you only need to hit them a few time before they are down, and there is a good chance that their attack power are simply not enough to make up the difference. Against a Mighty Glacier, you can easily land a lot of hits and they can still survive easily, even without a lucky dodge or two. They only need to land one or two attacks and snag a victory because of a last minute attacks. That being said, whenever your fought Pixies, Tigers, or Hares, consider them as a chance to get an easy win before fighting the Golems or Gaboos.
Combining. With the right combination formula, and proper knowledge you can produce a ridiculously powerful newborn monster and combining the training aptitude of 2 different monster can produce a pretty satisfying result, not to mention it also alters lifespan, lifetype, and guts regeneration rate giving a lot of customization possibility. The catch is when we say proper knowledge we do mean PROPER knowledge. The first and second games take it further since the result is randomized; be ready for Save Scumming (especially if it's a monster with worse probability such as Ducken. Get ready to do it, a LOT).
In the DS game, Kawrea drills are ludicrously broken. Due to the way the Fall drill map is designed, it is possible to get over 300+ points of Life in a single month, effectively making your monster the tank to end all tanks.
Good Bad Bugs/Game-Breaking Bug: A double whammy of a bug in Monster Rancher Advance 2. If you save, turn off the game, and turn it back on quickly, your monster will recover some Fatigue and Stress—meaning that doing this repeatedly means your monster will never get tired! The only problem? In a cosmic No Fair Cheating moment, this is due to a memory-clearing glitch that, if repeatedly exploited, results in your actual physical game cartridge breaking so that it no longer saves games properly. Ouch!
In Monster Rancher DS, combining a monster's main type with the ??? subtype of an -Ish monster will get you a unique sub-breed of whatever the main monster was. This actually isn't meant to happen, as it was intended that -Ish monsters could only be combined using their main types. But as you can guess, it's a pretty awesome exploit.
Monster Rancher 2 has the Swim Bug in the NTSC version of the game. The Swim drill calculates the stats gains from Life instead of the actual defense stats. Thanks to this, Fragile Speedsters like Centaurs and Jokers become FAR more durable, while the high Life-point ones such as Gaboo become Lightning Bruisers. Sadly, this ruins the defensive capability of the Stone Wall Arrowheads and the Mighty Glacier Golems.
The Japanese version of 2 has the Fairy Hare glitch. Thanks to a decimal error, the Speed of Fairy Hares was actually ten times greater than the monster's listed Speed stat. The Android game My Monster Rancher references this in the Fairy Hare's description.
Hilarious in Hindsight: The description for the Radial Niton, a special Niton that looks like a red racecar, states, "It is said there was a play called "Cars" in the ancient era." That was from Monster Rancher 2, released in 1999.
MR DS changed the save system; no longer can you save and immediately continue, or load your previous save while playing. Now saving means you automatically quit the game. And quitting without saving has dire consequences...
Surprisingly, the most notable example in the series belong to one monster, a Gaboo. Many players cried over Oakleyman's Straight and Ordorf's Acid Spit and its deadly Kick; it got worse when you notice that its stats are geared perfectly to become the kind of enemy you hate to fight against.
That One Boss: More like "that one monster". Especially in the earlier games, certain computer-controlled opponent monsters were noticeably harder than others.
In 2, essentially every Rank had one of these. In S Rank, every single monster is "That One Boss." And the Major 4, the Final Bosses of the game, are worse.
In E rank, where you usually start out, the most dangerous opponent is Oakleyman, a Gaboo. Most Gaboos you fight throughout the game have high Life, but sucky accuracy with their attacks. Oakleyman, however, has Straight, which is a very hard-hitting move at this point (It's actually a mediocre C/D-level move), high Dodge rate, and high HP. And worst of all, his Straight always seems to hit right when it would screw you over the most, making this a really good example of The Computer Is a Cheating Bastard. This makes its a perfect example of a Wake-Up Call Boss.
Any Mighty Glacier enemy in general, especially if you're not abusing the defense calculation of the game. Read That One Attack entry for the details.
Bonus Boss White Mocchi, Most, has all around high stats and a good move pool. Tough, but par for the end-game course. However, Mocchi has the innate luck ability (which is never hinted at whatsoever in the game) where the higher the Guts of the move targeting it, the better its chances of dodging it, making spamming your strongest low-cost moves the best strategy for dealing with Most. Of course those get neutralized by its high speed stats.
The higher tiers of the IMA vs FIMBA battle in Monster Rancher 2. Given to how rare they are and how hard to find the battle itself is, they're not as well known as Oakleyman or Most, but they are possibly one of the most frustrating monsters to fight. All of them have 700-750+ stats, effectively making them Lightning Bruisers. However, one of the more absurdly powerful ones is a Hare/Plant hybrid named Hammed, fought in the S-Rank. Unlike other Hares, it's custom designed to be a defensive beast, with 800 Defense (second highest stats) and 991 Intelligence— 8 less from the Cap— effectively making Int-based moves, usually effective against Hares, ineffective thanks to how damage calculation works in this game. Against Hammed, Power-based moves the way to go, forcing you to fight the exact opposite of the way you would fight a Hare.
The other S-Rank FIMBA monster that is That One Boss is Akirel, statistically the most powerful monster in the game (800+ in all stats save Skill). Unlike Hammed or Most, Akirel has no special tricks: it will simply smash your monster into the ground using its most powerful moves while dodging your counterattacks. Surprisingly amongst the three IMA vs FIMBA high tier monster, it's the ONLY one who has a Weaksauce Weakness. It only has its base attack as its range 4 move.
Saza A., the Rank D boss monster in Monster Rancher DS is notoriously difficult. Statistically compared to how your monster is at that time, he's even harder than the rank A boss monsters.
Complete Monster: Moo. Created to be a Super Soldier to end the last war, he feeds off of hatred and lives to bring it forth in others. To that end he corrupted countless monsters, destroyed many villages, and killed countless people—and possessed Holly's father, using his connection to her to further his own goals. As Tiger put it, Moo is pure evil.
Brian Drummond, who voiced Tiger of the Wind, would latter go on to voice Andrew Waltfeld in Mobile Suit Gundam SEED. Waltfeld's nickname? The "Desert Tiger". What do his troops pilot? Four-legged mecha that roughly look like blue tigers.
Must we refer to villainous Mooks as "baddies" in every single context, guys? For the kid protagonists, sure, maybe, but the king of evil probably shouldn't call his own minions "baddies".
In an odd case of Bowdlerization helping, the uncut version of Genki hitting Pixie in the face. The animation for it is unintentionally hilarious.
Ahem... "the evil Moo." The Big Bad ends up a lot less intimidating when most American kids associate his name with Old McDonald.
Some Anvils Need to Be Dropped: The anime's anti-war message really hits home after you see what war did to the planet in the past, and how it affects the Monster Rancher world in the present day. The backstory has humans who grew proud and destructive, creating Monsters for anything that would suit their wants. Eventually they created Moo in an attempt to end the last war, which ended up nearly destroying the entire planet until they created the Phoenix to stop him—and what it took to defeat Moo involved destroying virtually everything. When Moo returns to finish what he started, great sacrifice is required yet again—this time on a personal level, with the Searchers fusing together to become the Phoenix, and their consciousnesses ceasing to exist.
Episode 73 has Mum Mew screaming that she likes herself just as she is when Moo's soul starts to consume her and the others. After an entire season of buying exercise gadgets and hating being called old, when her life is on the line Mum Mew accepts herself and her body image.
Viewer Gender Confusion: Mocchi. Let's face it, being cute, pink, and voiced by a voice actress confuses the issue.
Villain Decay: Durahan was introduced in the second season as Moo's powerful and terrifying Starscream, with an army of monsters at his command which were creepily kept in cold storage until he had use for them. Third season rolls around, and he becomes the Big Bad... and also more of a joke, thanks to being saddled with a Goldfish Poop Gang and being reduced to a head.
Visual Effects of Awesome: It is very well-animated. If it's raining, for instance, the characters get a soft, fuzzy outline. Ditto with effects for fire and energy beams.
Woolseyism: Sometimes the dub's edits worked in its favor. In Tiger's battle with Grey Wolf, for example, the English dub added effectiveness by cutting out some of the battle with the Cabalos, devoting time to a flashback of the brothers' time as pups.
Pixie's torturing of Mickey in the uncut episode 10 clashed with the Searchers forgiving her so quickly and with her later characterization. While the uncut version gave Genki a more justified reason to punch her, punching her just for breaking a promise was believable given his childish nature, as well as his later statement that it was wrong to hit her over it.
"Eternal Worm", in the Japanese version, had Allan watch the heroes attack the Seed Sisters for about a minute after they killed his Worm before joining the fray. The English version had him jump in more quickly, which makes more logical sense.
Moo's tormenting of the heroes in "Tears". The uncut version has him shocking Pixie many, many times, with the final time being enough to get them all to hate him. While the dub cuts out him hacking off her wings beforehand, him taunting the heroes to get a rise out of them explains why Tiger was able to snap Big Blue out of it at first—and shocking Pixie afterwards was enough to push them over the edge.
In another case of Bowlderization making things more intense, Moo's beam attacks against the Dragon army. They're clearly hit, and in the uncut version they spiral to the ground like airplanes. By removing that, the dub implies they were vaporized on contact. Given Moo's an Expy of Godzilla, including the nuclear weapons metaphor, it works quite well.