Mallice appears as a large-headed giant, with a tuft of bright orange hair, deep red eyes and blue streaks down his pale face.He wears a yellow cape, a red vest, and blue-green shorts, with an arsenal of stakes stuck in them. He wields a giant wooden hammer with a red swirl painted on each end.
In the game, he seems to have an affiliation with Moody Mary. Despite that he calls her is his daughter, as he says after your fifth visit through infinite tunnel, He's really a manifestation of her nightmares.
One of his main attacks are using a giant hammer to pummel a single ally. His technique is summoning a stone onto one of your Yo-Kai He also has an attack similar to Cap'n Crash, where he swings his colossal hammer and hits each front row Yo-Kai 4 times. He also has the ability to summon stakes that both draw attacks away from him (although this can be avoided by using a pin) and prevent you from turning your Yo-Kai Wheel. Finally, he can summon an ultra-powerful meteor from the sky to severly damage one of your Yo-Kai.
"Derukuitataki" roughly translates as "loose nails whacker". It refers to the Japanese idiom "the nail that sticks out gets hammered in" (出る杭は打たれる, derukui ha utateru), equivalent to the English "the tallest poppy is cut down first".
"Mallice" is a portmanteau of "Mallet" and "Malice" emphasizing the fact that he is a nightmare entity.