Morgana is strong against Riven
While snared, Riven is unable to use two of her abilities, meaning if you snare her as morgana, implying that she doesnt have merc treads, she can only ult and do melee range attacks for 3 full seconds. i have died as riven countless times due to being snared in a bad spot. long duration snares and stuns screw her up. of course, this is implying that you actually hit her with your cc. that's why you pick morgana, if anyone can dodge that every time, they are a god.