"Let's Meet Sonic" is the 12th episode of Season 3 of OK K.O.! Let's Be Heroes and the 104th episode overall. It is a crossover episode that features Sonic and Tails from the Sonic the Hedgehog franchise.
When world class hero Sonic the Hedgehog visits the plaza, he teams up with K.O. to save the day. 
At Gar's Hero Supply & Bodega, K.O. enthusiastically prepares to defend the plaza while Rad and Enid decide to sleep the day after staying up all night playing video games. As K.O. warns them about what they might miss, the legendary speedy hero Sonic the Hedgehog arrives in the shop with his sidekick, Miles "Tails" Prower. K.O. begins geeking out over meeting one of his childhood heroes and shows the blue blur some of his fan art that recaps the duo's previous adventures. Sonic is impressed with K.O.'s encyclopedic knowledge about his achievements and offers the young fan the chance to be his "new little buddy," which Tails believes is a sign he's being replaced.
Sonic reveals that he came because he found a flyer that said Gar's Bodega had "the best chili dogs in the multiverse." When K.O. examines the flyer, he notices Darrell and Jethro on it. The two robots pop out of the flyer and kidnap the unconscious Rad and Enid before speeding back to Boxmore. Sonic and Tails agree to help K.O. rescue his friends after hearing that Lord Boxman is very similar to their archenemy, Dr. Eggman, and pursue the Darrell and Jethro to the factory.
At Boxmore, Lord Boxman chastises his robots for delivering Rad and Enid instead of Sonic. His plan was to kidnap Sonic so the other villains would take him more seriously and to use the hedgehog's speed to power up his machines. He then takes Rad and Enid to the next room and challenges the three heroes to dash through a loop de loop. Though Sonic and Tails are very experienced with these structures, K.O. offers to go first since he believes the next room could be a trap, but struggles to run through it. Sonic suggests using his signature technique, the Spin Dash. When K.O. can't seem to pull it off, Tails suggests visualizing an end goal, as doing so helped him achieve the technique when he first met Sonic. K.O. focuses on his goal of rescuing Rad and Enid and successfully manages to Spin Dash through the loop de loop.
In the next room, K.O. is snatched by Lord Boxman and placed into an unknown machine. Sonic and Tails arrive and notice that the machine is powered by the Master Emerald, which Lord Boxman acquired by tricking their friend, Knuckles. He reveals that the device is a robotocizer and uses it to transform K.O. into the robotic Metal K-O. Metal K-O begins chasing Sonic throughout the factory with his enhanced speed and some of the techniques Sonic and Tails taught him along the way such as the Spin Dash and Light Speed Dash.
Metal K-O eventually corners Sonic above a large water container since he knows Sonic can't swim. With Tails' help, Sonic gains the upper hand and knocks Metal K-O into the water. However, it causes Metal K-O to short circuit and he begins to sink. Sonic dives in and restores K.O. to normal by breaking his robotic shell, but the two start drowning. Fortunately, they are rescued by Tails. Tails is still bitter about Sonic supposedly replacing him with K.O., but Sonic clarifies that him calling K.O. his "new little buddy" doesn't mean K.O. is his new sidekick, but a good friend, and that Tails will always be his ultimate partner. An upset Lord Boxman plans on crushing Rad and Enid, but Tails hacks into the machine to allow Sonic the chance to snatch the two before he turns it on the villain.
Sonic and Tails take back the Master Emerald and attach it to their plane, the Tornado. As they leave, Tails tells K.O. it was fun hanging out and apologizes for getting jealous and Sonic tells him to stay cool and have some chili dogs ready next time. Before the episode ends, K.O. realizes he hasn't learned a valuable lesson yet.
The episode ends with a "Sonic Says" segment, a public service announcement that appeared at the end of every episode of Adventures of Sonic the Hedgehog. Using Rad and Enid as an example, Sonic warns children to avoid staying up too late at night, otherwise they could sleep through life and miss out on meeting people like him, which as he puts it, is "no good."
- Metal K-0 (debut)
- Sonic the Hedgehog (debut)
- Miles "Tails" Prower (debut)
- Mr. Gar (mentioned)
- Jethro (non-speaking)
- Lord Boxman
- Mario (drawing)
- Shadow the Hedgehog (drawing/indirectly mentioned)
- Knuckles the Echinda (drawing/indirectly mentioned)
- Doctor Eggman (mentioned)
- Cream the Rabbit (mentioned)
- Roger Craig Smith and Colleen Villard reprise their roles as Sonic the Hedgehog and Miles "Tails" Prower, roles which they have held since 2010 (Smith) and 2014 (Villard).
- Coincidentally, they are both the longest-running voices for the characters.
- This episode was announced at San Diego Comic-Con on July 19, 2019.
- This is the fifth crossover of the show as the previous crossover episodes were "A Hero's Fate", "The Power Is Yours!", "Crossover Nexus", and "Monster Party".
- According to Toby Jones, this ended up being the "self contained episode that will reveal itself in time".
- Metal K-0 is meant to be the redesign version of K-0 who debuted from "OK A.U.!".
- This is the final full crossover episode in the series.
- On July 11, 2018, Ian Jones-Quartey tweeted about his visit at SEGA which may infer that development of this episode started around that time.
- On April 4, 2019, Toby Jones tweeted that he and Ian filmed the end credits shot of K.O. running from a new background. A red square was placed as to not spoil further content. It is revealed that it is Sonic and Tails who were covered by the red square.
- The concept for a Sonic crossover was planned during Season 1.
- During one of the Sonic Official Live Streams, it was stated that they tried to squeeze in a reference to the announcer from Sonic Colors, particularly, the lines "Good, Great, Awesome, Outstanding, AMAZING!".
- Sonic asked K.O. about if the Bodega sells chili dogs. Joff had went to the Bodega before about chili dogs in "Be a Team". It seems that K.O. has been unaware of what chili dogs are.
There are several references to the Sonic the Hedgehog mythos:
- The Adventures of Sonic the Hedgehog and other Sonic television series:
- The music used for the title card is a Sega Genesis version of part of "Hall of the Mountain King". "Hall of the Moutain King" is also used in the theme song of the animated series. It also plays throughout the more intense moments of the episode.
- Sonic came to the plaza to try out some chili dogs, which is his favorite food in the cartoon and all subsequent media.
- Darrell's laugh is derived from Scratch.
- Sonic's quip of "Gotta lightspeed keed", is a direct nod to his catchphrase.
- When Darrell and Jethro arrive to Boxmore, Lord Boxman says, "Excellent, promotions are in order!" The way he pronounces "promotions" and his motions during it are a reference to Eggman giving himself a promotion in the original cartoon, which became a popular internet meme.
- Lord Boxman referring Sonic as the "fastest thing alive" is a nod to the "Sonic SatAM" theme song.
- The Roboti-Making Machine is based off Dr. Robotnik's Roboticizing machine from "Sonic SatAM", "Sonic Underground", and the aforementioned Archie comics. Sonic even makes the connection when he realized that KO's been "Roboticized".
- Lord Boxman referencing Darrell and Jethro as "Dumbbots", and him briefly blurted out "I hate that hedgehog!" towards the end are catchphrases that Dr. Robotnik said to his henchman.
- Coincidentally Jim Cummings, voice of Lord Boxman, also voiced Dr. Robotnik in "Sonic SatAM" and the pilot of "Adventures of Sonic the Hedgehog".
- The crushing machine built by Lord Boxman is based on a similar machine built by Dr. Robotnik in the pilot and credits sequence, and he even gets flattened the same way.
- K.O. refers to Tails as "Way past cool", which is one of Sonic's many catchphrases.
- The ending of the episode featured a 20-second life-lesson skit hosted by Sonic, which directly references the "Sonic Says" segments shown at the end of each episode. The segment's topic is similar to the "Sleep" short and Sonic quoting "That's no good!" is a direct reference to the infamous "Sexual Harassment" short in which the latter also became a meme.
- The Sonic the Hedgehog OVA:
- When K.O. tries to Spin Dash, Sonic lounges in the same beach chair he was using in the OVA in the scene where Tails tries surfing.
- The chase between Sonic and Metal K-O is an homage to the chase between Sonic and Metal Sonic in the OVA and Stardust Speedway in "Sonic the Hedgehog CD".
- Sonic attempting to rescue Metal K-O from the water is an homage to Metal Sonic's death scene in the OVA. Metal K-O's last words, "There is only one 'little buddy'" is a callback to Metal Sonic's, "There is only one Sonic."
- The video games:
- The episode opens with K.O. making two iconic poses of Sonic from Sonic Adventure and the original Genesis game. He also does Sonic's impatient foot tapping that happens when the player doesn't pick up the controller.
- K.O. unwittingly references Sonic 3D Blast when tells Rad and Enid that they'll never know when a famous hero will "3D blast" through the bodega doors.
- Sonic's entrance music is part of the song "Live and Learn" by Crush 40 from Sonic Adventure 2. K.O. also says "live and learn" later in the episode when Tails apologizes to him.
- Tails' theme is a remix of Emerald Coast from Sonic Adventure.
- The title card to the special is reminiscent of Sonic the Hedgehog 2.
- K.O.'s fan art references the events of Sonic the Hedgehog 2, Sonic Adventure 2, and the Mario and Sonic at the Olympic Games series.
- Sonic pushes Tails out of frame, and he comes flying from above in the next shot, a reference to how Tails' CPU dies and comes back in Sonic the Hedgehog 2 and Sonic the Hedgehog 3.
- Several of Sonic's techniques in the game are used such as the Homing Attack, Super Peel Out, Light Speed Dash, and the Spin Dash.
- Tails' yellow handheld device is the same one he's used for various purposes since Sonic Unleashed.
- Tails' backstory of his first meeting with Sonic is lifted from the Sonic the Hedgehog 2 manual.
- After K.O. clears the shuttle loop, he passes a goal post which transitions from an exit sign to showing his face, which references the goal posts in the Genesis Sonic games.
- The Master Emerald appears, having been taken by Lord Boxman.
- The design of Lord Boxman laboratory has similar design to Chemical Plant Zone in Sonic the Hedgehog 2, mainly the loops and double helix pipes.
- When Sonic and Metal K.O. use the Light Speed Dash during their race, the background bears a strong resemblance to the hexagonal Special Stages in Knuckles Chaotix.
- Metal K-O tries to take advantage of Sonic's inability to swim. When Sonic attempts to rescue K.O. underwater, a variation of the infamous drowning music from the Genesis games is heard.
- Sonic and Tails leave the plaza on their plane, the Tornado, with a device attaching the Master Emerald to it, similar to the ending of Sonic 3 & Knuckles.
- The final shot of the episode fades into blue while fading out, a reference to how levels faded when you started and finished them in the original Sonic the Hedgehog.
- Shadow the Hedgehog: He is mentioned by K.O. as the Ultimate Lifeform and appears on one of his drawings battling Sonic, referencing their battle in Sonic Adventure 2.
- Mario: When K.O. shows his drawing of Sonic winning the Summer and Winter Olympics, a mustached Italian-American plumber in a red hat (also Nintendo's official mascot) is shown crying that he lost next to him.
- Dr. Eggman: The evil scientist is mentioned by Sonic during their chase with Darrell and Jethro. Lord Boxman also says he went to college with Eggman.
- Knuckles the Echidna: Lord Boxman mentions how he tricked the "Little Red Fellow" into giving him the Master Emerald, which Sonic and Tails aren't surprised about.
- Metal Sonic: Metal K-O's name and design are based off Sonic's robotic counterpart.
- Cream the Rabbit: She is mentioned as an example of one of the little buddies Sonic has other than K.O. She is the only one who is directly mentioned by name.
- Other media:
- The comic that Nanini takes from Genesis is the Archie Comics run of Sonic the Hedgehog entitled "Sonic Quest".
- The way Sonic says Eggman is "the worst" is a reference to Jean-Ralphio Saperstein, a character from Parks and Recreation played by Ben Schwartz. Ben Schwartz is the voice of Sonic in the live-action Sonic the Hedgehog movie.
- Sonic's pose during the end of the Sonic Says segment was based off the infamous smug-looking Sonic panel from the Archie Comics' Sonic issue "What's the Point?" which became an internet meme.
- Sonic's leg is colored tan for one single frame during his grand entrance.