One of my most memorable plays with Brother Xavier was at the end of Dunwich Legacy, where I was facing a big 5 health enemy, and had Brother Xavier in play.
I played upgraded Dynamite Blast, which put 3 damage on me (well, on Brother Xavier) and then 3 plus 2 on the enemy. Not that memorable in terms of fluking a lucky draw from the chaos bag, but testless 5 damage in a single action was incredible.
No, what made it memorable was thematically I think we can all work out what Brother Xavier did. What a noble sacrifice.