If the spell has any mandatory additional costs, those must be paid to cast it.
For one thing, the mechanic has a ton of different options, and getting players to venture three or four times every turn would not only melt their brains but also take away the feeling of progress that's so much fun in going slowly
The best sequence of actions would be to cast 2 Creatures in your 1st Main Phase, Convert into Prowl, Stoic Strategist, and then attack as a 5/5 Creature that can Exile up to 1 other tapped Creature or Vehicle
(8/25/2015) If a replacement effect will cause cards that would be put into a graveyard from anywhere to be exiled instead (such as the one created by Anafenza, the Foremost), you can still put an exiled card into its opponent's graveyard

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