Elizebethan form of the colloquial 'innit'. Used loosely during Shakespearean times as a form of a) mutual aggreement between friends, b) to emphasise/reiterate ones resolve c) express/ reinforce a fondness/solidarity between ones cronies. Most often used among men. Marry may be accompanied by other such forms of agreement i.e 'ay', 'forsooth' and the like.
Henry: (gasp), by God the north London totty is out in force today!
George: Marry - looks like we're in for a smashing afternoon!