There are a lot of great inclusions that can be targets for this, including Cloister Gargoyle, Plaguecrafter, Burnished Hart, and Clattering Skeletons
If some of the attacking creatures leave the battlefield while Mangara's triggered ability is on the stack, use the player or planeswalker they were attacking before they left to determine whether you draw a card
One strategy for countering defensive power is to use spells that do not target
The key is to identify the function of an expensive staple and find an affordable card that does the same core job
Time Walk is one of the strongest cards of the Power Nine, as it gives the player an entire extra turn for the measly cost of two mana
Although Clone strategies can be sometimes overdone, I like them for their ability to scale to the other decks in the pod