Phyrexian Processor

As Phyrexian Processor enters, pay any amount of life.
{4}, {T}: Create an X/X black Phyrexian Minion creature token, where X is the life paid as Phyrexian Processor entered.

The Brothers' War Retro Artifacts

As Phyrexian Processor enters the battlefield, pay any amount of life.
{4}, {T}: Create an X/X black Phyrexian Minion creature token, where X is the life paid as Phyrexian Processor entered the battlefield.

From the Vault: Lore

As Phyrexian Processor enters the battlefield, pay any amount of life.
{4}, {T}: Put an X/X black Minion creature token onto the battlefield, where X is the life paid as Phyrexian Processor entered the battlefield.

Duel Decks: Phyrexia vs. the Coalition

You can pay 0 life if you want, but it's not useful most of the time.