Onechanside

is a new form taken by Yo-kai introduced in the Yo-kai Watch! anime series and Yo-kai Watch 4.

Information
In the middle of a tight situation, the user of the Yo-kai Watch must activate the Yo-kai's hidden power called the Onechanside. But they never know what to expect, whether it would be good or bad.

This mechanic behaves similarly to the Shadowside one, as the wielder of the Yo-kai Watch Elder needs to insert the Yo-kai Ark and turn it the opposite way from the regular summoning and then tap it on the watch's interface. This only happens in actual confrontations, as shown in YW005 Venoct did not actually fight Casanono and in YW006 as Blazion only talked to Siro.

Trivia

 * It's possible that it may have been based on the Chance Spell from the Final Fantasy games.