Into Verdant Cavern

You then exit the Pokemon Center and head towards the big cave with a sign that says "Verdant Cavern: Designated trial site for the island challenge". Illima steps out of it to greet you.

"Welcome to my trial," Illima says to you, "Please note that the Pokemon here are quite fierce. I hope you brought lots of Potions and stuff, 'cause once you go in, there's no going back until the challenge is complete. Join me when you are ready."

You enter the cave and it almost looks like a little jungle in itself, but instead of grass inside, it's just rock.

"Let me explain the basics of this Trial," Illima says to you, "In this trial, you are to defeat 3 Pokemon that lurk in these dens. Once you're done, reach the next area of the cave and collect the Z-Crystal on the pedestal when you see it." A fierce Pokemon roars loudly in the distance. "Oh my," he says, "I forgot to mention the really strong Pokemon lurking here, known as the Totem Pokemon! It will be your greatest obstacle to overcome. Oh yes, please do not catch Pokemon here until you finish the trial. Let us begin, shall we?"

(Illima's Trial starts! This guide will be focusing on the Pokemon Sun aspect, which means the Pokemon here will cover mostly Yungoos and Gumshoos. If you're playing Pokemon Moon, I believe it will be Alolan Rattatas and Raticates, which is a lot easier, I would think.)