Introduced in generation two of Pokemon, Sun Stones only can evolve five Pokemon out of the total of 898. Finding the right Pokemon for the stone can be a needle in a haystack without looking up answers online. With each new generation that adds more Pokemon, it will only get harder as well.
The Sun Stone typically evolves Grass-type Pokemon, as they make for most of the Pokemon to use the stone out of the five. So while some correlate the sun with fire, it is better to think of it in terms of how the sun helps plants grow.
In Pokemon, a Sun Stone is usable in terms of their generations from generation one, two, five, and six. While Sun Stones can easily be found in the Sword and Shield games using the Digging Duo brothers, the pick-up ability, and/or getting them from wild Solrock, the Pokemon Sun Stones can evolve may be more of a challenge to hunt down.
5 Gloom To Bellossom
From generation one, Gloom is a Grass and Poison-type Pokemon. It is a little unique as it can branch out to two different final evolution forms: Vileplume and Bellossom. Vileplume is achieved through a Leaf Stone and has always been that way since the first games. Bellossom was introduced later in the Johto generation, along with the Sun Stone itself. So Gloom can only evolve to a Bellossom with a Sun Stone.
Gloom is pretty easy to find in Sword and Shield. They can be found in the over-world at the Giant's Cap, Giant's Mirror, and North Lake Miloch. They are also hidden in the grass at Axew's Eye when the weather is cloudy. For the highest spawn rate, it is recommended to go to the third area of Giant's Cap during a thunderstorm. Of course, players can also start off with an Oddish and just let it evolve into Gloom at level 21.
4 Cottonee To Whimsicott
This part Grass and party Fairy-type Pokemon was introduced in generation five. It actually has the lowest Attack stat of any Grass-type Pokemon, which gives the player all the more reason to want to evolve it.
There are not many choices as to where to catch Cottonee in Sword and Shield, as there is only one location in all of Galar where they spawn. Luckily, the spawn rate is high at 40 percent. Though it is important to know, the Cottonee have no over-world spawns. They can only be found randomly in the tall grass. The location is the Stony Wilderness, and only when the weather is cloudy. The Cottonee there are between levels 27 and 29.
3 Sunkern To Sunflora
Sunkern is a pure Grass-type and is a very weak Pokemon, so players will want to evolve it with a Sun Stone as soon as possible. It has the lowest base HP and lowest overall base stat total of all Grass-type Pokemon. It is tied with Lotad for lowest Grass-type Defense stat. For lowest Grass-type Special Defense, it is tied with Bellsprout and Seedot. It does not even end there, as Sunkern is even tied with Blipbug for the lowest base stat of all (that's right, not just Grass-type) first-stage Pokemon.
Unlike Cottonee and Gloom, Sunkern is not found anywhere in the Galar region. It is not available in the two DLCs either, so Sword and Shield players do not have to worry about this Sun Stone user.
2 Petilil To Lilligant
Petilil is a lot like Cottonee, as it was introduced in the same generation, is a Grass-type, has one evolution stage, shares the same base stat total, and uses a Sun Stone to evolve. They are also often exclusive to opposing games. For example, Petilil was available in Pokemon White, White 2, Moon, and Ultra Moon while Cottonee was in Black, Black 2, Sun, and Ultra Sun.
Sword and Shield broke the exclusivity trend between these two Pokemon though. Petilil can be caught in either game, but only for players who have the Isle of Armor expansion. Within that expansion, Petilil can be found on Honeycalm Island both over-world and in the tall grass. It could take a little bit, as the spawn rate is only up to 16 percent.
1 Helioptile To Heliolisk
Helioptile is an outlier in the Sun Stone family, as it is not Grass-type. Instead, it is Electric and Normal-type (a type combination no other Pokemon has). This makes it the only non-Grass-type to evolve through a Sun Stone. Its design is based on a lizard, and lizards tend to love basking in sunny spots.
Helioptiles can only be found in two locations in Galar. Their highest spawn rate at 40 percent is at the Giant's Mirror during thunderstorms. With a 29 percent spawn rate, they can also be found at Route 6 during any kind of weather. They can easily be found in the over-world at either location.