Using the Yo-kai Watch
Before you can befriend a Yo-kai you must find them with the Yo-kai Watch. With the Yo-kai Watch's radar, players can track down invisible Yo-kai throughout the city. The radar needle will move clockwise into the red as you get closer to a Yo-kai, and the letter will change letters depending on the Yo-kai rank. Use the Yo-kai lens from the Watch until a purple gauge fills up to reveal a hidden Yo-kai.
Only six Yo-kai medals can be held in the Yo-kai watch at a time. The six medals are tied to the six Yo-kai that can be used in battle. You can swap out these Yo-kai with others you've collected in the Medallium. If you don't want a certain Yo-kai anymore, you can choose the Drop option to part ways with them forever.
After clearing out certain quests your Watch Rank will increase. Increasing the Watch Rank will allow you to open more Watch Locks around town and find higher-ranked Yo-kai using the Yo-kai Radar.
Rank D Challenge
The Rank D Challenge is tied to the Timers & More story quest. It will be unlocked automatically. See that page for a full walkthrough.
Rank C Challenge
The Rank C Challenge will become available during the What Dad Forgot story quest. You must find and defeat Signibble in Academy Shortcut, Suspicioni by Frostia's Place, and Tantroni in the Delivery Bay.
Before starting this quest you can begin the the Rank C challenge to power up your Yo-kai Watch. Head to Timers & More in Blossom Heights and speak with Mr. Goodsight to begin the quest. Next, head to Downtown Springdale to find and defeat three Yo-kai. You cannot defeat any random Yo-kai. You have to search for specific Yo-kai with blue flags over their heads.
Signibble can be found in the alleyway behind the Foundation Academy on the north side of Downtown Springdale. The Yo-kai will be waiting up the stairs.
Suspicioni can be found by Frostia's Place on the west side of Downtown Springdale. The Yo-kai will be hiding behind a few boxes in the middle of the alley.
Tantroni can be found in the Delivery Bay on the east side of Downtown Springdale. The Yo-kai will be waiting up the stairs on the east side of the alley.
After defeating all three Yo-kai, return to Timers & More in Blossom Heights to complete the quest.
Rank B Challenge
The Rank B Challenge will become available after completing the Rank C Challenge. Like before, you must find and defeat three Yo-kai. This time the Yo-kai are Tengloom at a Construction Site, Flumpy at the Shopping Street Narrows, and Mad Mountain in the Abandoned Tunnel.
Tengloom can be found at the Construction Site on the southwest side of Downtown Springdale. However, you must go at night or the workers will prevent you from entering. The Yo-kai will be waiting at the north side of the first floor. You will have to go up to the second floor, jump down the hole at the southeast side, and then walk north to reach the Yo-kai.
Flumpy can be found at the Shopping Street Narrows on the west side of Shopper's Row. This is the small alleyway to the east of Flower Road. The Yo-kai will be waiting down a small alleyway that branches off of the main path.
Mad Mountain can be found at the Abandoned Tunnel in the northwest part Mt. Wildwood. A small puzzle must be completed to reach him. The first cart at the entrance is broken down. Walk over to the cart on the right and take it across the track.
Head northwest to a lever at a dead end. Pull it to switch rails for the next mine cart. If you don't pull this lever, the mine cart will take you to a treasure chest.
Backtrack and cross the short bridge to the east. Take the third cart across the track further east. Fight the Leadoni to obtain a Leadoni Wheel. After the battle, continue north to find Mad Mountain.
After defeating all three Yo-kai, return to Timers & More in Blossom Heights to complete the quest.
Rank A Challenge
The Rank A Challenge will become available after completing the Rank B Challenge. Like before, you must find and defeat three Yo-kai. This time the Yo-kai are Quaken, Benkei, and Alhail. All three are located in the Springdale Underground Waterway.
Quaken is located near the entrance by the east river in Uptown Springdale. Enter the underground waterway and follow the path to the north to find the Yo-kai.
Benkei is located near the entrance to the southeast of the Sunshine Station in Blossom Heights. Enter the underground waterway and cross the steps to the north to find the Yo-kai.
Alhail is located near the entrance by the river on the west side of Breezy Hills. Enter the underground waterway and follow the path to the northwest to find the Yo-kai.
After defeating all three Yo-kai, return to Timers & More in Blossom Heights to complete the quest.
Rank S Challenge
The Rank S Challenge will become available during the Post Game. Like before, you must find and defeat three Yo-kai. This time the Yo-kai are Impass, Appak, and Timidevil. All three are located in the Yo-kai World.
Timidevil is located in Hungry Pass. To reach Hungry Pass, you must fall off the bridge passed the first gate. There is a break in the bridge about half way to the second gate. The Yo-kai will be waiting out I the open to the southwest.
Impass is located in Liar Mountain. To reach Liar Mountain, you must fall off the bridge passed the second gate. There is a break in the bridge shortly after the second gate. The Yo-kai will be waiting out in the open far to the southwest.
Appak is located in Hooligan Road. To reach Hooligan Road, you must fall off the bridge passed the third gate. There is a bread in the bridge half way between the third and lord's gate. The Yo-kai will be waiting around the middle of the area. The area is split into several roads. Appak will be standing on the road second from the left.