The analysis of a phrase

A royal family member of Amber and one of the Courts of Chaos, the protagonist can shapeshift.
The colossal creature, Dweller blocks a path not to let sorcerers pass.
It drawed a smoking line before it a while ago and told him not to pass it.

It similed. "I not only eat sorcerers, I eat their magic, too. Only a being torn from the primal Chaos can make that calim. So come ahead, if you think you can face that."
"Chaos, eh? Torn from the primal Chaos?"
"Yep, There's not much can stand against it."
"Except maybe a Lord of Chaos," I replied, as I shifted my awareness to various points within my body. Rough work. The faster you do it the more painful it is.
Again, the rattling of the tin sheet. [from Dweller]
"You know what the odds are against a Chaos Lord coming this far to go two out of three with a Dweller?" it said.
MY arms began to lengthen and I felt my shirt tear across my chest expanded and expanded. . . .
"One out of one should be enough," I replied, when the transformation was complete.
"," it said as I crossed the line.
["Trumps of Doom" of The Great Book of Amber by Roger Zelazny]
I'd like to know what "go two out of three" menas here.
Thank you in advance for your help.