The Monster Flower is a limited, mythical crop that was added in the Halloween Event.
How to get
It can be obtained through the Halloween Merchant with a price of 10,300,000 or 399 .
Appearance
The Monster Flower appears to be a crimson-to-maroon four petaled flower with dirty peach lips in the middle and yellowish-grey teeth, supported with green leaves.
or 399 
.