"wicked purpose" is correct and usable in written English.
You can use it to refer to a wrong or bad purpose, such as "She committed the crime with a wicked purpose in mind."
Wicked Wicked (Young Vibez).
It is no accident that one non-literary meaning of "plot" is, as the OED has it, "a plan or project, secretly contrived by one or more persons, to accomplish some wicked, criminal, or illegal purpose; a conspiracy".
Factors found to often reinforce the network include respect, mutual understanding and shared purpose such as tackling a wicked problem [ 12, 16, 17].
In one sense chess is a wicked game: Even the naïve moves accomplish more than the simple purposes they seem to be intended for.
Within these wicked problems may lie a company's most compelling and profitable driver: A global purpose to save the world.
Knox states that his purpose was to demonstrate "how abominable before God is the Empire or Rule of a wicked woman, yea, of a traiteresse and bastard".
My wife is a wicked, wicked person.
