Shielded Aether Thief
Creature — Vedalken Rogue
Flash (You may cast this spell any time you could cast an instant.)
Whenever Shielded Aether Thief blocks, you get 
(an energy counter).
, Pay : Draw a card.
Conflict breeds opportunity.
Illustrated by
Aether Revolt#44UncommonEnglishLegality
Rulings
If Shielded Aether Thief somehow blocks more than one creature at once, you get only one .
is the energy symbol. It represents one energy counter.
Energy counters are a kind of counter that a player may have. They’re not associated with specific permanents. (Other kinds of counters that players may have include poison and experience.)
Keep careful track of how many energy counters each player has. You may do so by keeping a running count on paper, by using a die, or by any other clear and mutually agreeable method.
If an effect says you get one or more , you get that many energy counters. To pay one or more , you lose that many energy counters. Any effects that interact with counters a player gets, has, or loses can interact with energy counters.
Energy counters aren’t mana. They don’t go away as steps, phases, and turns end, and effects that add mana “of any type” to your mana pool can’t give you energy counters.
You can’t pay more energy counters than you have.