1) Acting like a scamp 2) Devilish 3) Impish 4) In an impish manner 5) Like Bugs Bunny 6) Meanly tricky 7) Mischievous in a playful way 8) Playful 9) Roguish 1) Arrant 2) Blackguardly 3) Dishonest 4) Mischievous 5) Playful 6) Roguish 7) Scoundrelly 
• (a.) Like a rascal; trickish or dishonest; base; worthless; -- often in humorous disparagement, without implication of dishonesty.
Ras'cal·ly (răs'k a l*lȳ) adjective Like a rascal; trickish or dishonest; base; worthless; -- often in humorous disparagement, without implication of dishonesty. « Our rascally porter is fallen fast asleep.» Swift. 
[adj] - lacking principles or scruples
roguish adjective lacking principles or scruples; `the rascally rabble`; `the tyranny of a scoundrelly aristocracy` - W.M. Thackaray; `the captain was set adrift by his roguish crew`