Bogan is an incredibly dirty fighter in battle, even without direct orders. Combining the underhanded tactics the dark-typing is known for with all of the inherent trickster-malice of the fairy-type and stuffing it into the body of a creature that can overpower a Machamp on even-footing makes for a ferocious opponent to begin with. The Grimmsnarl kept a lot of his mentality from when he was a Morgrem - it’s typical for Bogan to feign weakness and fear to lure an overconfident opponent in before wrapping them up in his hair and beating them down with powerful blows. If he sees a chance to strike an opponent in a more vulnerable spot, such as taking an advantage of an injured leg or disorientating them with a heavy blow to the skull, he’ll also take those without being ordered to do so.
It took a lot of work on James’ behalf to teach him how not to go overboard, however, and trust him enough to know when to go for such tactics himself. It’s instinctual for members of his species to either draw out the beating for sport or to turn those aggressive, underhanded strikes into lethal blows, and teaching him to push that mentality aside took many long, difficult months.
