Jevil.

Jevil, a courtier, is the royal jester from Chapter 1 of Deltarune. He decided to gain power, found a dark crystal, and went crazy. The guards managed to neutralize him and put him in a cage on the ??? floor. The main character (who could be either Kris or a fictional character) managed to collect all the key fragments and open the cage, revealing Jevil himself inside. After the player entered Jevil's room, they were nearly cut down by scythes that fell from above, summoned by Jevil. He has a Five-Spike Attack. Jevil teleports to random points to the left and right of the playing field and fires a volley of five spike bullets. The central spike targets the SOUL, and the projectiles fan out. To dodge, you must constantly move between the spikes.
Spiral Attack. Ten large bullet-like spikes appear around the playing field, one after the other, moving in a spiral toward the center (clockwise or counterclockwise). In the early phases, the direction of the spiral does not change, but later in the battle it may shift.
Heart Attack. Bombs with hearts fall in the center of the field. When they explode, four hearts appear, forming a square and rotating around the central point, flying towards the SOUL and going out of the field. Try not to go into the very center.
Scythe Attack (Devil's Knives). Four scythes oscillate around the center of the playing field, rotating in one of two directions. In one version, a large red scythe appears later: it can appear either at the top or bottom of the field and fly horizontally, causing damage on impact.
Carousel Attack. Rows of horses appear, moving across the arena from left to right, like a texture on a 3D screen. The final attack is that scythes fall from above, which must be dodged.

Jevil wears a purple and black jester's hood with horns and a small yellow bell at each end. Around his neck is a green and yellow jester's collar and a black cape; the colors of Jevil's collar match the colors of Chris's shirt in the Light World. As for clothing, Jevil wears a purple shirt with black sleeves and black triangles in the center and stripes on the sides, purple mittens, black pants, and green slippers.

It is implied that Jevil, like several other inhabitants of the Card Kingdom, is a playing card in the Light World. Jevil can transform into Devilknife,[2] and Susie refers to Devilknife's Light World counterpart as a "strange card" during the church sermon in Chapter 4. His position as the court jester implies that he is the Joker card; this is further supported by his claims that he can do anything, as the Joker is most often used as a Joker. Furthermore, his attacks combine attacks across suits, similar to how the Joker can be any card of any suit.

Character
Before Jevil went mad, he seemed to have a sense of humor[3] and was as good as his friend Sim at gaming.[4]

Despite his descent into madness, Jevil retains his eccentricity and zest for life. He has a sadistic sense of humor and views meeting others as a "GAME," which is likely why he was locked away. However, Jevil also holds a cynical outlook, believing everyone else is trapped.[5]
(it can kill the user)