His'tuun is a powerful eldritch being, one who seeks to expand its followers while imparting "the truth" on those around it. It burrows into a being's mind and projects all of the desires the creature has, with a simple message - all of these are possible, so long as you convert.
His'tuun's fight should be a bit of a build up. While His'tuun is waiting to enter this realm, party has been dealing with his three main followers - Ambition, Conviction, and Devotion. They should be well familiar with how those creatures work.
His'tuun will constantly be attempting to mess with the minds of those coming to kill it, converting them temporarily while trying to leverage that into a more permanent solution.
Use Impart the Truth very consistently. This is the fight's bread and butter. His'tuun converts people, commanding them around the map, all the while they're seeing nothing but happy thoughts in their mind. Their consciousness takes a bit of a back seat, living every dream they've had.
Aside from this, use Go Forth, My Follower to control the battlefield. His'tuun is all about messing with the mind, move units in a way that doesn't make sense.
Lastly, utilize the abilities of Ambition, Conviction, and Devotion to your advantage. Each of Hist'uun's followers have unique abilities that are useful in different scenarios.
His'tuun is confident, cocky, and yet warm and inviting. The very definition of a snake oil salesman, every word the eldritch being implants into your mind is dripping with charm. His'tuun only has one real desire - to convert everyone in the material plane to his followers. Humanoids are impractical in their current state, and the very notion of free will leads to dissent and corruption. His'tuun invites those around it to wake up, see the truth, and embrace the freedom of not having to choose.
While that is His'tuun's ideology, it does not shun those who think otherwise. Oftentimes, at first, His'tuun will actively debate with those who dissent. It's like a game to His'tuun - how long can it cause the creature to run circles around itself trying to prove their point.
Until it grows bored of the games, of course.
His'tuun is a being from another realm. Every few thousands of years, it's able to wiggle its way into the material plane and begin laying seeds. It's certainly not the strongest of beings, but has an uncanny agility to infiltrate the minds of humanoids, giving it the upper hand.
His'tuun has an obsession with control. It wants to take over the material plane and will stop at nothing to make that happen. Each time it's emerged in the past, it's been thwarted.
