Mining in proof-of-work blockchains is a lucrative practice, and revenue driven mining strategies in these blockchains, adversarial or otherwise, have been extensively explored. We present a new revenue maximization attack suite named ProphetChain, where a rational attacker leverages Blockchain Denial-of-Service (BDoS) to paralyze the blockchain network, with the intent of forcing the victim miners to pay a ransom before the network can regain liveness. We detail the ProphetChain attacks, and outline an analytical framework for optimal ransom transaction valuation as a function of the advantage of the attacker in the blockchain system.