Bossfight:
Written in Blood
This bossfight should be implementable in any fantasy context via a small plot twist or a detour.
Boss' Name: Fictio
Intro: A Door
For one reason or another, the hero(es) enter(s) an old library. Entire sections may have collapsed, but some are still intact.
As the hero(es) explore(s) the collossal library halls - books from floor to ceiling - they come across an eerie ward: The middle is illuminated through a gap in the ceiling; a pillar of whirling dust in the light calms as the hero(es) approach. Something moves between the shelves, makes a shuffling sound.
Footsteps then, shadows, and flickering light. Steady first, faster then. The light must be from a bonfire, or perhaps a lamp. Short as a stool comes around a corner, a gnome - lifts a dusty eyebrow. (yeah it's called the Yoda effect, I hope it worked)
The gnome claims to be a librarian. But where are the rest? They're dead - got killed by some "exPLODing jigsaw munstor!"
"Yeah, big fleshy munstor, kips boooomin' all the time
I can't believe it. Strange things happening. It's like fact and fiction has been all mixed up together in this library.. Well I was actually in the middle of something over here... Better be careful where you step, big guy!" The gnome returns supposedly back to a pile of books.
Funny thing is, if the hero(es) try to look for the gnome now, he has vanished; is nowhere to be found.
Searching the ward further one will almost literally (haha) stumble upon (or rather step on) a book that is so old it falls apart and pages crumble when touched. Underneath it is a pressure plate that when carrying the weight of a human opens an immense gate that for some reason has been blocked and covered by bookshelves. The feeble shelves ofcourse crash down on the hero(es) as this happens.
Recovering from this shock hit one will encounter a black gap which is the entrance to something. Yes, it leads down a pitch black corridor with a mouldy old smell. A cold, eerie breeze licks one's skin with something sticky in the air. "It's called fiction" booms a powerful voice. "Come hither, I shall read it out loud".
Villainography: FICTIO
Who is Fictio? Often encountered in dreams and literature, Fictio takes on himself many different names, appearances, and identities. He claims to be the incarnation of fiction, but scholars do not count that for a fact, since he made his first accounted appearances in literature very recently, and dream encounters cannot really be accounted for in the same scientific manner.
Scholars deny his objective existence, and for more than just that reason, Fictio is not a big fan of scholars.
Fictio will inevitably try to seduce or persuade his enemies, who will burn classical works just to get rid of him, that he is the very definition of fiction, and that with his seize of existence we would all lose our imagination, and our ability to dream. This ofcourse isn't fact, but fiction.
Tricks up Fictio's sleeve:
Dreamy Captivity: Immobilizes; waking nightmares (drains mana)
Fictional Aberrition: Summons random freak of imagination
Archival Trap: Sends the target to a random first letter destination within the labyrinthic library
Shapechange: Has no practical effect, but he does it frequently, often blink teleporting at the same time.
Other Spells: More as one pleases.
Spells Explanation: Within the library, fact and fiction is all mixed up, as the gnome mentioned. Fictio's story elements are real when he wants them to be. That is why he does not make mirror images or illusions, but summons monsters. They're fictional and factual at the same time.
His teleportation spells have to do with him being part of the library, and taking control over every ward. But he cannot teleport himself more than a short distance within sight. I don't know how this should be explained.
The Fight
Fictio can look in any way one likes when first encountered. It might even be random. As Fictio is a shapeshifter and a phase shifter, he is a highly elusive enemy who has not one face but many.
How to kill him? Whenever he takes the form of some defenseless being, like a dog, villager, or something, you can hurt him directly, but that is VERY rare. The rest of the time, you must just kill off his summoned freaks and find a source of fire. You will bump into the gnome at some point. He is dead, and his lamp is still glowing - it stands on top of a pile of books, and can be picked up by a hero. The lamp is useful if the hero has no fire-based spells; it can set certain objects on fire just like a fire-based spell. In this bossfight, some special books need to be burned. These books are hidden throughout the library. But beware, Fictio's monsters tend to be summoned near these books.
When all the books are burned, Fictio has only 1 shape which looks like some gooey ooze. In this shape, he can be hurt directly by anything, and is vulnerable to fire, but is actually more dangerous than before due to more aggressiveness and a acidic attacks. Kill him in this final shape, and it's victory.
Well, there are a few more complications. Fictio will make up new stories over time, meaning his literary works will respawn, as he regenerates life. Each book burned should take away a very large amount of his life, and when the same amount of life is recovered, a book should respawn.
You can include any kinds of traps in the library and be creative with the monsters that Fictio summons.
In the context of my intro story, you could use a "fleshy jigsaw moster that goes boooom" (self-detonating abomination), as the gnome mentioned, or you can just leave it out and rewrite the intro. It was really just an example.
I recommend using 1 dummycaster for all his spells, and let it cast a modified polymorph (edit: Hex) spell on him every time the spell expires, so he will periodically take a new form.
Enjoy playing around with this idea