mischievous

Causing mischief; injurious.

...; that good and bad actions at present are naturally rewarded and punished, not only as beneficial and mischievous to society, but also as virtuous and civious; ...

On the whole, therefore, he concludes that the point of indulgence at which these self-passions or self-affections begin to be mischievous to the individual coincides with that at which they begin to be mischievous to society; ...

Troublesome, cheeky, badly behaved, impish, naughty, disobedient; showing a fondness for causing trouble in a playful way and liking to have fun by playing harmless tricks on people or doing things they are not supposed to do.

Matthew had a twin brother called Edward, who was always mischievous and badly behaved.