Each time you cast a spel...can you tap as much black or white mana as u want to extort? Or can u only extort for one with each creature with each creature with extort. Like if i had a tithe drinker and casted a spell could i extort with just tithe for three? Or could i only do it for one...?
{Tithe Drinker}
You may only pay one for each instance of extort. But multiple instances stack (thanks to {Pontiff of Blight})
Once per creature
{Tithe Drinker}
"Whenever you cast a spell, you may pay B/W"
So "whenever" is the key word, you've casted a spell, you may extort once for that creature"
You've only casted one spell, so it only allows for one extort to trigger on each creature with extort.
Now if it was something that said, "you may extort and then you may extort again" on the text for the creature, then you could pay for extort twice whenever you cast a spell or if the creature has multiple instances of extort (ie Pontiff)
702.100a (http://imtgapp.com/forum/index.php?action=imtg;area=rule;number=702.100a): Extort is a triggered ability. "Extort" means "Whenever you cast a spell, you may pay {W/B}. If you do, each opponent loses 1 life and you gain life equal to the total life lost this way."
702.100b (http://imtgapp.com/forum/index.php?action=imtg;area=rule;number=702.100b): If a permanent has multiple instances if extort, each triggers separately.
The easiest way to think about extort is every time you cast a spell, each instance of extort from all permanents you control puts itself on the stack. When it resolves, you then have the option of paying b/w or not.
So extort needs to be paid for as soon as spell has resolved ?