Each creature spell you cast with mana value 4 or greater has blitz (If you cast this spell for its blitz cost, it gains haste and "When this creature dies, draw a card." Sacrifice it at the beginning of the next end step.). The blitz cost is equal to its mana cost.
Blitz costs you pay cost less for each time you've cast your commander from the command zone this game.
Vintage
Modern
less for each time you've cast your commander from the command zone this game.