Won on my 5th attempt with a 133 5/2/3 Venom.
Strat was to deny red, hoard green and yellow until the end, then fire yellow then green. Used some match damage boosts and +all AP.
First three attempts, I did not let Carnage make a single red match, and he still fired off Symbiote Scythes every time, because tinykitty cascades. Got close a few times, but didn't have enough green to finish the deal. Fourth attempt was so bad (cascading match-5s) I retreated by turn 6.
Finally got a friendly board, lots of yellow, and manageable amounts of red and green. Killing blow was 3x yellow for 2500 a pop, then 2x green to finish him off.
Reward: (already max covered, 1000 ISO)
Mine is a 5/1/1, so I'll need a LOT of greens to make this one work...