You don't need to have intense Legendaries or fully-evolved third-stage Pokemon on your team to put up some respectable numbers in special defense. There are plenty of completely unevolved Pokemon at the beginning of evolutionary lines that have very decent special defense base stats.
Sometimes you're not far enough into a game to have access to Legendaries or the final evolutionary stages of certain Pokemon, so you have to make base stage Pokemon work. Fortunately, there are plenty of them with great base stats, including special defense.
If you find yourself unable to take on strong gym leaders that are hitting hard with special attacks, considering throwing an Eviolite on one of these great options for special defenders.
10 Lileep
Most of the Fossil Pokemon base stages have fantastic stats, especially in physical and special defense, since they're (almost) all Rock-types. Lileep is no exception to this. The pre-evolution of Cradilly and one of two options of Fossil Pokemon from Generation III, Lileep has fantastic special defense, with a base 87 points.
Its evolution, Cradily, also has a respectable base special defense of 107. This isn't record-setting by any means, but it is very useable in a lot of situations.
9 Shieldon
Another Fossil Pokemon on this list is Shieldon, which specializes in high defensive stats, and works as a counterpart to the other Gen IV Fossil, Cranidos, which focuses on attack. While not quite measuring up to its 118 base physical defense, Shieldon still has a very nice special defense stat of 88, just a point ahead of Lileep.
Evolve this small little dinosaur, though, and it'll be a special wall. Bastiodon has an insane special defense of 138, which will tank many different types of special attacks with ease.
8 Duskull
A bit of a surprising entry on this list is Duskull, which is by no means famous for its base stats. Poor Duskull only has a base stat total of 295, averaging around the same number of many Baby Pokemon. Interestingly, a full 180 of this 295 is in the defensive stats, as both physical and special defense are a base 90 points.
That's amazing for an unevolved Pokemon, but it, unfortunately, comes at the cost of its other stats. Duskull only has 20 in base HP, 25 in speed, 30 in special attack, and 40 in physical attack.
7 Drowzee
Psychic-type Pokemon have always been known for their amazing special stats. That, paired with its physical bulkiness, makes it no surprise that Drowzee, the Psychic-type from Generation I, has a very respectable special defense stat. Like Duskull, it has 90 base special defense.
Luckily, though, it doesn't sacrifice the rest of its stats. They're not amazing, as its base stat total is still just 328, but they're distributed a bit more evenly. That can be good or bad, of course, depending on the situation.
6 Nosepass
Basically a magnetic rock with a face, it's no great shock that Nosepass would have good defensive stats. And, it has an extremely impressive physical defense base stat of a whopping 135. Its special defense isn't quite as good as that, but it's still a nice 90 points — the same as Duskull and Drowzee.
Interestingly, when it evolves, Nosepass swaps which defensive stat is better. Probopass has 145 physical defense and 150 special defense.
5 Mime Jr.
As mentioned, many Psychic-types are known for their special stats. Fairy-types are as well, so it makes sense that a Pokemon with both those types like Mime Jr. has a decent special defense stat. Like the past few entries on this list, Mime Jr. has 90 base special defense. That's especially impressive for a Baby Pokemon, as they typically have middling stats at best.
Which region you evolve Mime Jr. in will determine how much its special defense develops, too. Kantonian Mr. Mime has a base special defense of 120, while Galarian Mr. Mime's is 90. However, the latter can evolve into Mr. Rime, which has a base special defense stat of 100.
4 Type: Null
Type: Null is a Legendary Pokemon from Alola that was created by humans to be an Ultra Beast killer, so it's no surprise that it has the highest base stat total of any unevolved Pokemon that can still evolve.
Every one of Type: Null's base stats — except speed — are the same: 95. This includes its special defense. When it evolves, Silvally has all the same base stats except its speed, which increases from Type: Null's 59 to be the same as the rest at 95. So, its special defense does not improve.
3 Tentacool
Two of Tentacool's weaknesses are Psychic and Electric, both of which heavily favor special attacks. So, it can be annoying when traveling through water-based regions where Tentacool are plentiful, because it has very high special defense to counter its weaknesses. Maybe go for a Ground-type attack instead.
Despite middling stats in most categories (its second-highest is speed at 70), Tentacool boasts a powerful 100 points in base special defense. That's impressively-high for an unevolved Pokemon, and makes up about a third of its overall base stat total of 335.
2 Galarian Corsola
Introduced in Generation II originally, Corsola had very unimpressive stats for a single-stage Pokemon that was unable to be evolved. They weren't terrible, but they were just hovering around average in most situations. However, if it were able to evolve, many of its stats would be very impressive for a pre-evolution base stage.
Luckily, Galarian Corsola came along with its evolution, Cursola, making it so many of its stats (which are the same as Johtonian Corsola for the most part) are now pretty impressive. This includes its great 100 points in special defense.
1 Mantyke
Amazingly, the record-holder for this particular stat is a Baby Pokemon. Mantyke, the Baby pre-evolution for Mantine, boasts the highest base special defense stat of all unevolved Pokemon at a whopping 120 points.
It's unclear exactly why Mantyke has such high special defense, but it's surely very impressive. Mantyke is actually near the top of the list for all Pokemon in special defense. Though not quite at the very top alongside powerful Legendaries, Mantyke is higher than some Mega Evolutions, Gardevoir, Snorlax, and even Regigigas.