I am trying to brew up a campaign item of sorts for my game (seven level 6 characters currently). They recently assaulted the lair of a criminal mastermind with a hold over an important trade route city, discovering him to be a gray slaad in disguise. They defeated him, but one of the items in the lair which they found was a very unique magical book, which at the time seemed to be protected by magic that wouldn't allow it to be identified or opened. Below is what I have for the book so far, and I'm hitting a brick as to what it should do.

A gilded and gem ecrusted tome with a metal case that conceals the pages with an elaborate locking mechanism. Attempts to pick it, if failed against a DC 30 deal 3d6 lightning damage to anyone in contact with the book. It is immune to all damage and magic while protected, except for a Wish spell, or Divine Intervention from a sufficiently powerful deity. Dispel magic cast against it are a DC 16. Once dispelled or unlocked, the locking mechanism vanishes, and the book can only be damaged by acid, necrotic, or radiant damage from a 5th level spell or higher, or an attack from a 9th level creature.

The incoherent pattern of gems and recesses on the cover, once unlocked, shift to transform and reveal the title as The Dreamwalker Tome. The pages are thick golden tablets, not paper sheets, of which there are only 6, each about a half-inch thick and shimmering with reflected light.

The book can only be opened and gazed upon by a willing creature. To creatures looking at the book from afar but not touching or holding it, the pages appear dull and blank.  Each page, when opened to, has a different effect:

Page 1: Reader must succeed on a DC 15 Wisdom saving through or be put to sleep for 1 minute. Attempts to wake them up by mundane or magic means deal 1d6 psychic damage to the reader. They experience nightmares of the person trying to wake them actually trying to attack them. When they wake up, the reader slams the book closed and cannot open it for 24 hours. On a success, the reader can never again be affected by this page, and can now read the page as normal, which has [insert cool effect here]

I'd like some help coming up with ideas for what each of these 6 pages might do or contain, and what effects/saves the reader will have to withstand in order to gain them. Because it belonged to a Slaad, containing a means of teleporting to Limbo makes some sense. I think I'd like a page to give access to some extra-dimensional space, perhaps even a structure, containing belongings of the Slaad, which may have its own perils. Outside of that, I'm struggling to decide on what I like. Any ideas are welcome.

Give it the ability to extract or make spawning stones in slaadi

I like the spells dream or dream of the blue veil but if you want an extra dimensional space you can have it use  something like astral projection to represent dream walking to limbo where they find an alien structure inside that once they explored fully gives them a fragment of limbo to make their own dream demiplane as storage places that they can access at night when they sleep.

hmmmmmmmmmmmmmmmmmmmmmmmmmmmmmm. what if the slaad intended to use it as something of an escape route. teleporting the reader to some stronghold or even another plane?

this idea is kind of silly and might not work, but what if it beamed the reader up to a spelljamming ship?

gave them something like the diviner wizard's third eye?

I like these spell ideas a lot. Definitely going to play off of some of these ideas. Also makes me want to dig into some higher level spell lists for more ideas. Thanks!

And yeah I did have in mind having one page be some kind of escape route, possibly Limbo, possibly some other lair the bad guy would have had.

First, make it clear that you need to remove the lock before a willing creature can open it.  Right no= it kind of implies that any willing creature can ignore the lock and just open it.

I like the dream spells idea, presented earlier.

In addition, I would suggest that it gives advantages to any sleep or dream related saving throws, including Sleep spells, Dream Eater's Waking Dream ability, and even the Dreamwalker's Charm of a Stone Giant Dreamwalker.

Finally I would suggest that you gain the ability to hide objects in your dreams.  When you go to sleep you can take any object(s) upto levelx5 lbs weight. into your dreams.  When you wake up, you can leave them, as long as the total weight remains below level x 5 lbs (total weight in dreams), or take any of that out.