Enchant Creature
At the beginning of enchanted creature's upkeep, it's controller sacrifices it unless he or she pays its converted mana cost.
At the beginning of enchanted creature's upkeep, tap it unless its controller pays its converted mana cost.
See Challenge # 128.
I wanted something that captured the flavour of trying to swim back up a waterfall, but it's a bit too wordy (and maybe out-of-pie). Any suggestions?
Oh, hmm. That first ability really isn't blue, though I do get the flavor you're going for.