This situation came up yesterday, and at the time I was convinced the card worked one way. I assumed his wording only prohibited him from contributing to the str total in a challenge ("counting" strength). I had another look at it again today, and am suddenly less certain…
If House Clegane Outlaw (with no power on him) is knelt for Game of Cyvasse during a challenge, what value is used for the comparison of "highest strength"? Is it "2" or "Null"?