The Emperor Crab's Surge is strong against elementals, which both the flower and the turnip are.
You pretty much have to fall asleep to get a crab killed in this fight.

Farmer Nishi, in Valley of the Four Winds. P/P Emperor Crab with Surge, Shield, and Healing Wave + two low level pets who can take one Sunlight from the Sunflower. Kill the Sunflower with nothing but Surge, Shield on the turn when the Turnip comes forward, heal while it is underground. Wait to take ...

1. Most definitely. I have four fossilized raptor hatchlings. Can't even give them away anymore.
2. Not that I have noticed or read about. It's all RNG.