Embercleave only technically costs that much because of its ability: it costs one less for each attacking creature you control
This is a bit simplified, but here's how a store manages Magic product
As the triggered ability resolves, first the next opponent in turn order (or, if it's an opponent's turn, the opponent whose turn it is) chooses a creature they control, then each other opponent in turn order does the same, knowing the choices made before them
They do indeed look like energy cards because they were
It basically means that everyone can put their biggest thing into play for free, and while theres always a chance that shell die before you get to take advantage of that ability, itll definitely earn you some favor
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