Design an adult coloring page portraying the shadow cat encountering an ancient magical portal materializing under the moonlight. The portal emits an ethereal glow, revealing a passage to an unknown and mysterious realm. Frase na página: "At the threshold of mystery, a portal opens." Prompt: "Illustrate the shadow cat before a magical portal in black and white, which has appeared under the moonlight. The portal should emit an ethereal glow, creating a mysterious and intriguing atmosphere. The scene should arouse curiosity about the unfamiliar realm that unfolds beyond the portal. The image should be rich in details, without additional shadows or colors, allowing readers to express their creativity while hand-coloring and be drawn into the magic of the mysterious encounter.