"3 mana seems worth the benefits if you were bringing force hammers to take out conjurations." Two problems. 1) unless combined with jinx your opponent always has a chance to place a wall to protect his conjuration 2) you leave the enemy conjuration on the board one more round, that means a vine tree deploys once more, a deathlock prevents another round of regeneration, and an obelisk collects one more round of upkeep. 3) Every time I've attacked a conjuration I've regretted it. They are tough for their cost, and really only worth killing opportunisticly when your opponent is being defensive. But if a conjuration is nasty enough then the previous problems make force hammer a better solution.
