Iseires, Sorcerer Supreme

Iseires, Sorcerer Supreme has Beast (When this creature enters the battlefield choose a permanent you control. All your creatures get +{x}/+{x} where {x} is chosen creatures converted mana cost.)
When Iseires, Sorcerer Supreme blocks, attacking creature gets -{x}/-{x} where {x} is Iseires, Sorcerer Supreme's power.
Iseires, Sorcerer Supreme cannot die from
blocking.