Evolving a Pokemon is usually as easy as training that critter up until it hits a specific level.
Things are never easy, though, are they? A number of Pokemon in Sun and Moon will only evolve under very specific circumstances.
In this article, we list those circumstances. Aren't we nice?
If you're looking for Eevee, we've detailed all of its evolutions in a special article, here.
Rattata - Raticate
If Rattata levels up to level 20 or higher while it's night time in the game, you'll get Raticate.
Sandshrew - Sandslash
Give Sandshrew an Ice Stone and it will evolve into Sandslash at the next level. You can get one of these stones at the Poke Pelego, or in Po Town on Ula'ula. It's by the swimming pool, accessed via Shady House.
Vulpix - Ninetales
Same as above. Give Vulpix that Ice Stone to unlock Ninetales.
Magneton - Magnezone
Magneton is one of a handful of Pokemon who will unlock a special evolution if you level up at Vast Poni Canyon, which is on Poni island.
Cubone - Marowak
Get Cubone to level 20, or higher, when it's night time in Alola to turn this Pokemon into Marowak.
Nosepass - Probopass
Level Nosepass up while in Vast Poni Canyon to get this evolution.
Yungoos - Gumshoos
Yungoos must become level 20, or higher, during the day time to become Gumshoos.
Charjabug - Vikavolt
Like Nosepass, you need to level Charjabug up while fighting trainers or wild Pokemon at Vast Poni Canyon.
Crabrawler - Crabominable
This special evolution will only happen if you level this Pokemon up while at the top of Mount Lanakila, which is on Ula'ula Island.
Rockruff - Lycanroc
This can go one of two ways. First, Rockruff must hit level 25 (or higher). If it's day time and you're playing Pokemon Sun you'll get Lycanroc's Midday Form. If it's night and you're on Moon you'll get the Midnight form.
Salandit - Salazzle
Salandit turns into Salazzla at level 33 - but only if that Pokemon is female. If your Salandit is male you're stuck in adolescence forever. Ouch.
Steenee - Tsareena
If Steenee knows the move stomp, and then levels up, it will turn into Tsareena. Steenee can learn stomp at level 29 so make sure you don't skip that move!