Thirty pieces of silver

Asmodeus opened his hand; it had two thumbs on it, flanking five fingers.  The fingernails were opalescent and unusually thick, and spurs of bone poked through the knuckles at each joint.  In the palm of his hand was a literal handful of pieces of silver.  Each one looked slightly greasy; a rainbow shimmer came off them and the design on the faces of the coins was hard to focus on and read.
"And I just take one?"  Travis's voice was hesitant, catching in his throat.  His hands stayed firmly pushed into his coat pockets and the threadbare garment pulled tight around the back of his neck.
More than one if you like, said Asmodeus.  His voice seemed to come from far away and yet at the same time it was like hearing someone whisper in your ear.  Travis pulled a hand free from a pocket to rub at his left ear.  I am not ungenerous.
"There has to be a catch," said Travis.  "You're Asmodeus.  You wouldn't give power away just like that, there's got to be a catch."
Very well, there's a catch, said Asmodeus.  His eyes sparkled; they were grey and deepset with crow's-feet at the corners.  There was a hint of a smile on his face and it was like looking at a cheerful grandfather.
"I knew it!" said Travis.  He paused, and then balled his hand up into a fist and shoved it back into his pocket.  "What's the catch then?"
You'll be able to use a portion of my power, said Asmodeus.  For any purpose you choose.  However, no other King will be able to offer a portion of their power while you have a portion of mine.  They're mutually exclusive.  We have quantum mechanics working on the why of it right now, in fact.  Working hard.
"I don't think I understood much of that," said Travis.  Honesty was, in his book, the best policy, but even he would have to admit that his book was a short one with easy words and a big font.  "If I take one of your coins then no other demon will give me a coin as well?"
King is the preferred term.  The writers of the Bible found it apt to... heh, demonise us, but we were mortals too.  And Kings, for that matter.  I can introduce you to Nebuchadnezzar if you like?  Or perhaps Balthazar?
"They sound like drinks, not Kings," said Travis.  His eyes were fixated now on the coins and he had a hungry look on his face.  "Whose got the best coins then?"
Me, obviously.
"Yeah right, but you would say that wouldn't you?  How do I get more of you here so I can have a... like a... thingy, you know!"
Auction?
"Yeah, sure, that'll do."
Take my coin.  You'll have power then over a number of other Kings.  Take more than one coin and you'll have power over even more Kings.
"Hang on, this can't be right."  Travis rocked back and forth on his feet, his fists clenching and unclenching inside his coat pockets.  His left eyelid was flickering with muscle spasms.  "Each one of those coins is like one-thirtieth of your power.  What if I just take them all?"
Of course you may take them all.  Asmodeus's hand moved a little closer to Travis and the coins jingled seductively.  Though there are only twelve there.  And each coin represents only 1% of my power.
"So there's a hundred in total?"
There are thirty in total.  It is a – significant – number.  And I am not fool enough to give away all my power, child.  I might need it, after all.
"Right, right," said Travis.  His eyes were almost vacant now and a droplet of drool was forming at the corner of his lip.  "I can have one right?  Mine.  To keep."
Oh yes, said Asmodeus.  But don't forget that there's a catch.
"Yeah, sure," said Travis.  His hand came out of his pocket and he lunged at Asmodeus's hand.  He pulled a single coin from the pile and held it up.  "Mine!"
Asmodeus made the other coins disappear nearly instantly and a wide grin spread across his face.
Mine, he echoed.