Let Sleeping Pokémon Lie! (Japanese: 寝る子は強い、ネッコアラの秘密！The Strong Sleeper, Nekkoara's Secret!) is the 56th episode of the Sun & Moon series, and the 995th episode of the Pokémon anime. It first aired in Japan on December 28, 2017 and in the United States on May 5, 2018.
Our heroes are curious about the origins (and sleep habits) of Principal Samson Oak’s partner Komala. After telling the students how they met, Samson shows off Komala’s impressive skill at battling in its sleep!
They get another lesson in sleep when Jigglypuff shows up at the Pokémon School! As always, its song makes everyone sleep, and they wake with angry scribbles on their faces…everyone except Komala. That gives Samson an idea…
When Jigglypuff returns, Komala joins it in song. This makes Jigglypuff fall asleep, and Komala doodles on its face! Rather than being grumpy when it wakes up, Jigglypuff seems to think this is hilarious. Komala has a new friend!
Litten and Lycanroc are in the middle of training. Lycanroc uses Rock Throw and Litten returns with Ember. Soon after, however, Professor Kukui calls Ash for breakfast and instructs him to call Professor Burnet. Ash then jumps into the sea and dives down to meet Burnet with Munchlax and Rotom. Burnet shows Ash a Pyukumuku, but Ash pokes it and then gets attacked by its fist and subsequently rises to the surface. Munchlax finishes all of its Pokémon food before everyone else before Kukui reminds Burnet she has a business trip today. Kukui helps Burnet pack and Ash leaves for the Pokémon School. A Jigglypuff can be seen floating above Ash as he travels to school.
At the playground, Ash and his classmates are battling each other, Togedemaru is chasing after Snowy, and Lillie doesn't know what to do to stop it. Kukui advises the gang to give clear commands to their Pokémon so they know what do to. Ash and Kiawe are battling and Litten uses Fire Fang. In retaliation, Kiawe makes Marowak use Iron Head before Komala rolls into the middle of their battle. Kukui comments that it fell from the tower again. Lana asks when and what it eats and Kukui shows the gang some leaves which people and other Pokémon don't like but they are Komala's favorite food. Komala eats the leaves. Kukui says that the leaves make Komala constantly sleep. Ash tries to wake Komala up with a big scream but stays asleep. Samson Oak appears and tells the gang that Komala changes its expression because of the dream it is having. Rotom says that Komala never leaves its log and that it receives it from birth.
Samson Oak tells the gang how he met Komala. He was taking a walk when he finds a Komala with no log running all across the road. With no log, Komala rolled around in its sleep and Oak gave Komala a fruit that looks like the log to stop the problem. Instead, Komala jumped on Oak's head and slept comfortably. Oak then made a log but Komala didn't like it so he let Komala stay on his head. As Principal, Oak had to ring to school bell but then one day Komala jumped on the log and started ringing the bell. Oak let Komala keep the log that was for ringing the bell. Komala learned to ring the bell at the correct times. Ash wanted to battle Komala.
Team Rocket are seen strolling through the forest complaining about their Proto-Koffing problem. They want to capture special Pokémon or Ultra Beasts for the boss and think about the rewards. Bewear finds them and as they run away, they find a Jigglypuff with a microphone. It uses Sing and they all start to fall asleep when Jigglypuff gets annoyed and draws funny faces on them.
Back at the playground, Ash is fighting Komala with Litten. Litten uses Ember and Scratch and Komala dodges both attacks. Komala uses Wood Hammer and knocks Litten down. Kiawe suddenly jumps in and sends out Turtonator. Turtonator uses Flamethrower and Komala dodges. Turtonator uses Dragon Tail and dodges again and then Komala used Rapid Spin. Ash decides to use his sleeping Rowlet and against Komala this time. Ash tells Rowlet to use Leafage, Tackle, and Peck but fails to respond. Then suddenly, the Jigglypuff appears. The whole gang awake and realize they have funny faces and laugh. Kiawe notices that Jigglypuff didn't draw a face on Komala. Rotom Dex recorded whilst asleep and Komala dodged Jigglypuff and then it left.
Jigglypuff comes back and knocks Ash and Kiawe over whilst trying to put a funny face on Komala. Jigglypuff sings again but the gang wear glasses that makes them look awake. But the glasses fall off and they have more faces. Again, Komala has no marks and Komala dodges Jigglypuff.
Oak decides to make Komala learn the song so it can sing it to Jigglypuff. Lana conducts all the Pokémon and they recite the song for Komala to hear. Komala learns the song but they all start to fall asleep except Komala. Jigglypuff returns and Oak wants it to sing again. The Pokémon all sing again but Jigglypuff has a funny face on it and the gang don't. Rotom Dex shows them the clip of Jigglypuff and Komala singing together. Then Jigglypuff falls asleep and Komala draws on Jigglypuff's face. Jigglypuff starts laughing when it sees its face in a bucket of water.
Team Rocket wakes up and they see their faces. As a result, they start laughing, after which Bewear takes them back to its den.
The Dare da? segment is a reference to the gag used in EP056, showing a silhouette of Jigglypuff seen from above. The gag was also a part of that episode's Dare da? segment in the original Japanese version.