devilish

showing the cunning or ingenuity or wickedness typical of a devil; "devilish schemes"; "the cold calculation and diabolic art of some statesmen"; "the diabolical expression on his face"; "a mephistophelian glint in his eye"

playful in an appealingly bold way; "a roguish grin"

in a playfully devilish manner; "the socialists are further handicapped if they believe that capitalists are not only wicked but also devilishly clever"