Converge — Gain control of target creature if its power is less than or equal to the number of colors of mana spent to cast Exert Influence.
Exert Influence is the newest incarnation of a “fair” conditional Control Magic effect, like Domestication. In this case, Exert Influence is bound by both power and by colors of mana spent with its Converge ability. Exert Influence will never take a creature with power greater than five, so it won’t be taking powerful Eldrazi, and with the Converge requirment, it will further be limited to decks with access to many colors of mana. With its new dual lands and manlands joining existing fetclands and painlands, Battle for Zendikar promises to allow four and five color decks, so Exert Influence will have the ability to shine. I see it as a fabulous tool for seizing control of Siege Rhino and its cohorts.
Exert Influence is not without a distinct advantage compared to the typical Control Magic, because it’s not an Enchantment but a Sorcery. Enchantments are always at risk of being destroyed, and control reverting back to its owner; this makes these cards much less reliable strategically, and a combat step risk. Exert Influence gains control of a creature permanently, and leaves the opponent without options. Gaining control of an opponent’s creature is a card advantage 2-for-1 and massive tempo gain, and Exert Influence cannot be undone.
Exert Influence is currently quite cheap, and off the radar, and while it’s not going to be a Standard all-star four-of in every deck that can cast it, it is going to play a role in the new five-color world, so it is not a card to ignore.