Bogatyr Blade

Weapon (battleaxe), rare (requires attunement)

This +2 battleaxe is crafted of ancient mountain stone and was a weapon of the first kings against the barbaric hordes that stood against them. As a bonus action, you can transform the bogatyr blade into a handaxe or greataxe, or into the form of an unremarkable pebble. The blade reverts to a battleaxe after 1 minute or when you spend a bonus action to transform it again, whichever comes first.

Whenever you strike a giant with the bogatyr blade, it takes one additional die of damage. You also deal this extra die of damage whenever you attack a creature using a rage effect (including the barbarian class ability) or when you hit a creature that is flanking you or that has scored a critical hit against you since the end of your last turn.