Heroic killing blow is the scariest thing the Bretts have. Perhaps taking a Heavens Slann or Tet to Curse of the Midnight Wind on an enemy knight character before engaging with your Saurus (or a dinosaur).
One thing just to check is that he hasn't taken a virtue on top of his magic allowance, it's an easy mistake to make. I'm assuming though he's got the Gromiil Great Helm and HKB. Things like the piranha blade are good, with AP and multiple wounds you only need one wound to hit to potentially kill him off and you can get your 4+ ward save still which you'll need. Otherwise as others have said arcane unforging are very good or things that ignore his armour like Spirit Leach.