Old blood on carnosaur with piranha, potion of strength, shield, and 5+ ward amulet.
Or take the burning blade of chotec if likely to be facing dark elves or skaven, then you can also afford a 4+ ward.
Alternatively ditch the magic weapon and take a great weapon for permanent strength 7 (S10 for one round - take THAT Necrosphynx!) and then you free up points for the dawnstone so you have a 1+ rerollable armour save, 4+ ward and 5 S7 attacks. That'll put a dent in pretty much anything. Plus he can't be thunderstomped because he's cavalry.
The only problem is getting to them - M7 is alright but not fast enough. If a monster is down to a couple of wounds left you could try a Skink Chief of a terradon with sword of the hornet (he'll need those rerolls to hit as he only has WS4) and a potion of strength. He can fly so will catch them no problem, and can reliably cause two or three S7 hits on them. He only costs 130 points. He'll die like a mosquito to any sort of retaliation or ranged attack though, so it's a one-shot attempt. Personally I wouldn't really use this method as anything other than a fun change of pace, as it's not generally going to be very effective - but it will be worth it when it is!
Finally, you could try using the Lore of Shadow and once you've tied up the monster with some Saurus or whatever, cast Occam's Mindrazor to make them S8. Even skinks would be S6 with the spell.
I'm sure there are other methods too. It's a shame the carnosaur can't be ridden by a Scar-vet. It's not bad as it's S7 and does D3 wounds, so seems custom-built to take on enemy monsters... but it's quite over-priced, is only T5 with low initiative, so will a) probably be eaten before it gets to strike, and b) stop you from using a Slann in anything but the highest points lists. If I could put a Scar-vet on one I'd definitely try it out.
