Peema Aether-Seer

The target creature blocks only if it's able to do so as the declare blockers step begins. If, at that time, the creature is tapped, it's affected by a spell or ability that says it can't block, or no creatures are attacking its controller or a planeswalker controlled by that player, then it doesn't block. If there's a cost associated with having the creature block, the player isn't forced to pay that cost. If that cost isn't paid, the creature won't block.

The amount of {E} you get is determined as Peema Aether-Seer's first ability resolves. If the greatest power among creatures you control is somehow negative, you don't get or lose any {E}.

The controller of the target creature chooses which attacking creature that creature blocks.