Tiso is an adventurer who seeks the Colosseum of Fools for the sake of challenge. He presumably fights using his shield, which he claims conceals a "deadly surprise."
He is arrogant, thinking of himself as an 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, the player never actually fights him, 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.
Pale thing. You wear that nail with ease. If you're in search of combat, you'll find no great warriors in this decaying burrow. I've heard an arena exists somewhere below. One built for our like. Meet me there and we'll test what skills you possess. I'll be heading down soon. Come and find me if you dare.
Hallownest... What challengers await in its ruin?
This little squib clearly fears me. I'd kill it right here, but it'd be too pitiful an end.
Second Encounter, Forgotten Crossroads Stag Station
Ehh. Pale thing. You use these old lines? Pathetic. A real warrior carries himself to combat. He has no need for such convenience.
Leave me be. It's the arena I seek. I've already wasted far too long on these cursed roads.
Those old stags could've been ferocious fighters. If only they weren't so servile...
Third Encounter, Blue Lake
Tiso is seen standing at the eastern shore of the Blue Lake, gazing over the water and expressing his dislike for peace and serenity.
Garrgh. What a calm place. It's action I want, vicious and deadly battle. This serenity is a bore.
So peaceful. So dull.
That place calls to me. Somewhere beyond this lake, perhaps?
Fourth Encounter, Colosseum of Fools
Tiso is found sitting on the bench below the Colosseum of Fools, looking at the ground as if waiting.
Pale one. You found it too then, this perfect place. I'll soon be entering the battle. Just taking a moment to rest first. Though few could truly challenge me, I'm hoping this arena presents the sort of brutal challenge I'm after.
I'll crush them all. Oh, and you. You'll see me at my deadly best. You think this shell a defensive arm? Well I'll give you fair warning, it conceals a deadly surprise. Pray you never find out what that is.
...The perfect challenge. I can already taste my victory...
Tiso is named after Tiso Spencer, the Kickstarter backer who designed him.
There is some evidence that Tiso may have been intended to be a Boss in the Colosseum of Fools at some point, but was scrapped later for unknown reasons, Possibly because his creator only had paid for an NPC and not for a boss.