So, going against a Drizzt, my opponent played a Watchwolf, eventually made the watchwolf legendary with Drizzt's Herald, and also gave it Relentless with a mystic weapon from a Stoneforge Mystic. When the watchwolf was revived from Relentless, it lost the legendary border, but when it attacked it still triggered Drizzt's hero power panther despite not appearing legendary. I would expect either a) the watchwolf should still appear legendary after revival to show that it is still legendary, or b) the watchwolf attack shouldn't trigger the panther. I've attached a screenshot from my game that shows this state.