So the fight would work a little like sans' fight
If you try to attack him he dodges, you just gotta keep attacking
ATK 30 DEF ?
After 10 dodges
At one point he will tell you how strange it was for you to directly attack him and that he will make you pay
At that point he dosent dodge anymore, but teleports
At 15 dodges
He starts to attack faster and faster
Now dealing enough damage to 3 shot you
At 20 dodges
He starts to get tired, and the rest is pretty much the same as sans fight, just a lot longer
At the end when you hurt him, he will say:
"Oh, you actually hit me, what a shame, guess your the monster after all"
Phase two
ATK 100 DEF 100
He summons swords, but dosent dodge anymore
When he reaches half health:
"Well you are stronger than i thought! May i reward you?" - insane attack
Last phase - 1hp
"..."
"..."
"So thats it huh..."
"No..."
"I wont give up yet"
"If you've come this far...that means..."
"You really are the monster"
He summons a second sword, yes double wielder
ATK 200 DEF 300
Despite having 1hp he resists attacks
At the end, before he dies, he does one last final attack, similar to sans'
Then you hit him, killing him
Reward: The Traveler's Sword - ATK 100 Durability 1000 Ability: Absorbs magic to become stronger (for each magical attack absorbed you gain +5 ATK)