Definitions of devilish:

• adjective:   playful in an appealingly bold way
• adjective:   showing the cunning or ingenuity or wickedness typical of a devil

  Example: "Devilish schemes"

• adverb:   in a playfully devilish manner

  Example: "The socialists are further handicapped if they believe that capitalists are not only wicked but also devilishly clever"