The Library

After the initial rush of water several linches deep as the door was opened the flow has dwindles to a slow trickle. The fountain and aparently no longer woring drainage are the cause of the garden turning into a swamp. The room has a few objects covered in vegitation including a couple benches and small tables as well as a few other items so shrouded by the growth that if it was not for their regular shape and an ocasional spot of stone or metal beneath the leaves you might think it just another bush.

As you begin looking through the thick overgrown foliage Seren notes a small tendril pull back as a leaf is moved. Quickly tracing the motion more leaves are moves to expose a small slime that squirts a potent acid when exposed.
1 damage to Seren
Though the slime is small and not able to squirt far Seren suspects these are what have been damaging the plants. The slime likely keeps other pest away from the plants but if there are too many slime, as she suspects, then their acidic trails would scar the plant, matching what she noted earlier. As long as you search carefully you should be able to avoid further incidents with the slime, which try to get out of your way but are not fast nor smart enough to do so. Likely if you waded through the plant without caution you would soon be covered in acid burns.

Now that Seren is aware of the slime she is confident she can avoid them with caution and moves to look around the garden.

As you move beneath the ancient oak tree, leaves flutter and rustle. The sound of the leaves sounds like a faint scratchy whisper. Seek the book where pages rustle and branches speak. What knowledge does nature yearn to share? After you hear the phrase the whisper disappears no matter how you listen. Searching around the tree all you can find are the initials AL carved on a small knurl of wood at the base.

Continuing your search you find a pedestal. On it is a plaque identifying the creation of the library garden as a gift from Artenia Lien. On the back you find another smaller plack plaque that says
When the celestial dance is in harmony, you'll decipher their messages.

You get the impression this had nothing to do with the undead. They are a recent anomaly.
The celestial dance refers to the movement of bodies in the heavens, starts, planets, moons. Druids are typically closer to the nature of this world so this likely refers to something about the three moons of this world. It is common lore that the moons are associated with the three primal forces. Order(perfection vs entropy), Existence (creation vs oblivion), Change (static vs dynamic)