Though few could truly challenge me, I'm hoping this arena presents the sort of brutal challenge I'm after.
Tiso is an adventurer who seeks the Colosseum of Fools for the sake of a challenge. He presumably fights using his shield, which he claims conceals a "deadly surprise."
After the Mothwing Cloak has been acquired, Tiso can be found next to the well in Dirtmouth. He lightly hints at the Colosseum of Fools and expresses his urge to challenge the Knight. If he is never interacted with in Dirtmouth for the first time, he will never move from this spot for the rest of the game until finally listened to.
Tiso is seen standing at the western shore of the Blue Lake, gazing over the water and expressing his dislike for peace and serenity. If he is never interacted with in the Blue Lake, he will never move from this spot for the rest of the game until finally listened to.
Tiso is found sitting on the Bench in the warrior's pit of the Colosseum of Fools, looking at the ground as if waiting. He needs to be interacted with in the Colosseum and then a Trial must be done for him to move from his spot on the Bench. After this Tiso's corpse is found lying on a ledge in Kingdom's Edge.
He is arrogant, thinking of himself as the ultimate warrior and showing nothing but contempt for the weak. He almost pays no notice to the Knight until later on, and even then he finds them beneath him.
Despite his bravado, he is never actually fought, as he dies off-screen in the Colosseum of Fools, his body later found dumped by the acid pits at the bottom of Kingdom's Edge with the other slain warriors.