Slackerjack resembles Pierrot with purplish skin, round orange eyes with yellow scleras and two line markings running down, and a short mustache. He wears a colorful pierrot attire, with the left sleeve purple in color and the right sleeve red in color; the chest is purple, green, yellow and red stripped and the collar is yellow in the right side and green in the left side. The low part of his attire is purple and dark blue in color, with a star pattern, and ends in a wispy manner. He completes his attire with a pierrot hat, green and red colored in the sides. His most notable trait is the flute he carries, in a playing manner.
He plays his flute to manipulate people.
He was created by Gogogo Godfather with the UFO Stone. Slackerjack himself presumes he was likely created from Gogogo Godfather's "adult heart".
Yo-kai Watch 3
Slackerjack appears in Chapter 4 of Hailey's story, in which he lures small children with a tune of his flute, among them Hailey's little brother Riku. After being fought and defeated by Hailey and Usapyon, he confesses he was being a bit lonely and agrees to release the children.
In Chapter 9 he is revealed to be a member of the Gogogo Family, aiding them in their assault on New Youma City.
He can summon musical notes to protect himself. Said notes must be taken down.
Inspiriting the player's Yo-kai by playing a musical tune, causing him the confusion status.
Swaying the player's Yo-kai to change places in the field by playing another musical tune.
Attacking a single Yo-kai by causing an strident noise.
Launching a volley of big notes on either the left, center, or right sides of the field.
A Soultimate attack which slowly expands its rank on the sides of the field. The player must move his/her Yo-kai to the center to avoid damage.
His Japanese name is derived from "yamerunja" (Japanese: やめるんじゃ,"Stop it"). Notably the "ja" part of it is written with the kanji "邪", which can be translated as "evil". Adding to that, the "Yāmerun" (Japanese: ヤーメルン,"Yāmerun") part of his name is very similar to "Hāmerun" (Japanese: ハーメルン,"Hāmerun"), which is the Japanese name of the German town of Hamelin, where the fairytale of the "Pied Piper of Hamelin" is said to have taken place. Furthermore, "-sensei" (Japanese: 先生,"-sensei") is a respectful title used when adressing teachers, doctors, and the like.
His English name is a portmanteau of the word slacker and Cracker Jack; a term to describe an upstanding person, which is combined with slacker
He most likely pays homage to the "Pied Piper of Hamelin" fairytale.