Even if the cost of the spell or ability that waterbend is part of increases or decreases, you still may only tap artifacts or creatures to pay for costs up to the amount of the generic mana in the waterbend cost
Shadowborn Apostle is a human as well as a cleric, but you dont have to limit yourself to that strategy
Its also tough because they have a wide range of abilities
Find and Expansion have shown that Wizards of the Coast arent messing around with the rare split cards in this block, and Ravnica Allegiance looks to bring some similarly heavy hitters
Ive lost money on some of them, certainly, but Ive always had a chance to make at least 70-80% of my investment back
It's unsurprising that a black Wraith card wants to sup on your vitality, but hey, there are plenty of times when paying two life to draw a card is preferable to using up your precious mana