While piloting the Golgari Yawgmoth deck, Ive regularly ruined an opponents board simply by killing off their creatures/shrinking them enough to make attacking unprofitable, and Ive even proliferated an opponents Chalice of the Void from one to two to lock them out of casting a bunch of spells
Its definitely creepy, but that does nothing to detract from the stunningly drawn art on this Magic: The Gathering card
Letting you move counters around each turn will certainly open him up for some fun interactions (Luminous Broodmoth, perhaps?)
She is good enough too that it is usually right
Obviously they will not have sufficient mana in their next turn to just recast the spell in question and so they will have a dead draw coming their way
In general, thats not terribly productive, but if you have a creature with an ability that triggers when it enters the battlefield or when it dies, this lets you trigger it again