One of the finest parts of Pokemon designs comes in how deceptive they are. Sure, they can often be cute or cool or even just kinda dopey, but that's no indication of their power. Some of the strongest Pokemon are often the ones people least expect to hold incredible strength. By the same token, some of the strongest looking Pokemon aren't actually as menacing as they appear, being mostly harmless. It's a odd part of the series, but an important one.
When deciding the strength of a Pokemon, trainers will often do snap judgments based on appearances. Size, for example, will often mean that a Pokemon is bulkier. If a Pokemon has strong jaws or muscles, perhaps it can be considered to have a high attack. This is where deceptive designs will really catch trainers off-guard. In terms of bulk, there are some small or unassuming Pokemon that can take more hits than anyone could anticipate.
10 Shuckle
Although this Pokemon is hardly deceptive for veteran trainers, younger players may be surprised by just how bulky this bug-type is. As opposed to other bug-types making the best of a terrible typing, Shuckle is designed to be a fully-defensive Pokemon. It's a bit small, and its shell hardly looks that sturdy, but Shuckle is a Pokemon that can and will take every hit that gets thrown at it.
In terms of base stats, Shuckle's total is fairly low at 505. However, those stats are absolutely loaded into both of its defenses. It sits at 230 for both of them, although every one of its other stats is just pathetic, including its HP. No other regular Pokemon compete in either category, although some Mega Evolutions match it. Shuckle isn't a great Pokemon, but it is certainly a bulky one.
9 Carbink
A rock-type having high defense is hardly a surprise, and Carbink is just that. This gem-encrusted fairy-type Pokemon is far from the strongest, and its small size and stature likely makes it seem like it shouldn't be as tanky as it actually ends up being. More importantly, Carbink also has the specially defensive bulk that other rock-types lack.
Carbink's defense stats sit at 150 each, although its HP is a pitiful 50. This doesn't make Carbink an attractive option as a stalling Pokemon or a wall, but it can do the job fairly well. It can even increase that bulk further with Calm Mind, which allows it to pretend to be a dangerous threat. Alternatively, have it explode after setting up everything it needs to. A sad life for this little rock.
8 Umbreon
The Eeveelutions are surprisingly durable across the board. Even the more offensive oriented options like Flareon and Jolteon have respectable special defense. However, probably the most iconic of durable Eeveelutions is Umbreon. It has seen its days at the peak of competitive play, but mostly just remains a solid options of mid-tier teams in need a Cleric.
Umbreon's role as a cleric is one that it fulfills perfectly. With Wish and Heal Bell, it can work to keep other Pokemon healthy in single battles, and it can bust out a Foul Play to try and check Pokemon carrying lots of buffs. With its defensive spread overall and good typing, it doesn't live in fear of too much. Just keep an eye out for Pokemon with Taunt, since they turn Umbreon into an adorable paperweight.
7 Mantine
Mantine is a very unassuming Pokemon. It has a big happy smile on its face, and may end up getting ignored by trainers in favor of other, more common water-types. When looking at bulky Pokemon, water-types tend to populate the field and Mantine, despite its looks, fits into that category.
Its typing gives it a crippling weakness to electricity, but that ends up not being such a big deal. The most powerful and common electric-type attacks also happen to be special attacks, and Mantine boasts incredible special defense. It can take those powerful hits, and it certainly checks Pokemon that deal exclusively in water, fire, or grass-type moves. It may look a little dopey, but this manta ray and take a lot of punishment.
6 Sylveon
Another defensive Eeveelution, Sylveon is even more unassuming than Umbreon in terms of its bulk. While Umbreon may be a tad more menacing in its appearance, the adorable and powerful pure-fairy Sylveon doesn't seem like a Pokemon capable of taking hits. That is, of course, not accurate to just how effective Sylveon is.
Sylveon fills a similar role to Umbreon, since they share many of the same techniques. However, while Umbreon has little offensive presense, Sylveon is has a high enough special attack to do some serious damage in unsuspecting targets. With 130 special defense and 95 HP, it can take special attacks like a pro.
5 Pyukumuku
Pyukumuku is very Shuckle-esque in nature. It boasts a similar kind of statline, with high defenses and low stats in everything else. However, unlike Shuckle, it actually has an HP stat to talk about even if it isn't much. It even has recovery moves, something that Shuckle is lacking.
Pyukumuku has a base 130 in both defense and special defense. This little sea cucumber is very small in size, and uses that to ambush unsuspecting Pokemon in the wild. It's interesting to see that its lore in games fits its purpose in battle, although most trainers know what to expect with Pyukumuku. It won't defeat its opponent; it will make them want to quit.
4 Alomomola
Alomomola, which many people wish had just been an evolution to Luvdisc, fulfills a different role in party composition to Luvdisc. While Luvdisc has broken dreams of being a rain sweeper, Alomomola is confident in its role as a bulky water-type. In fact, it's likely a lot better than people give it credit for.
Alomomola has awful special defense, but solid defense and sky-high HP. It boasts one of the highest HP stats, sitting at 165 base HP. It has moves to stall, moves to wall, and moves to recover. While it isn't completely unable to defend itself either, it has no stats to back its moves up. Alomomola is a Pokemon that will catch a lot of trainers off-guard with its tankiness.
3 Chansey
Held items play an important role in Pokemon battles, often defining the Pokemon they are equipped to. One of the most powerful is the Eviolite, which increases defense and special defense of Pokemon that can evolve. In a twist of fate, this ends up making some not-fully evolved Pokemon better than their evolutions. Case and point: Chansey.
Blissey and Chansey have been long-defined by their ability as a special wall, boasting astronomical HP and and special defense. However, the Eviolite amplies these traits on Chansey more than the bonuses it gets from evolving. Chansey can even take physical attacks easily, something that it was never able to do before. It's the ultimate wall and has been since Gen 5.
2 Munchlax
Munchlax, the baby form of Snorlax, is a Pokemon that shouldn't be as tanky as it actually is. However, its small size is completely deceptive, even when it tries to play outside of Little Cup matches. In Little Cup, it is a demon wall to be reckoned with.
Munchlax boasts incredibly high HP and special defense for a baby Pokemon. Boosted by an Eviolite, its power is unmatched in Little Cup despite its weaknesses to fighting attacks. In casual play, getting walled by a Munchlax early on is something that can be expected due to its high HP stat. It's quite tanky for its size, that's for sure.
1 Toxapex
Competitive battlers will likely understand the power of Toxapex, but newer trainers may not find much to be afraid of. It certainly looks like a fortress of sorts, a sea urchin ready to poison its foes. However, that's an understatement to the tankiness of Toxapex.
Toxapex has incredible defensive stats, with 152 defense and 142 special defense. It has bit of HP as well, meaning it isn't just raw defense like Shuckle. More importantly, it has self-recovery and special protection moves that allow it to live longer than it has any right to. And on top of all of that, it has Regenerator to keep itself healthy. Toxapex is notorious for a reason, even if at first glance it doesn't pack bulk. This thing is a tank to end all tanks.