Remnodok, Cryptic Shaper

At an optional extra cost, you may pay
half of your life.
When Remnodok, Cryptic Shaper enters the battlefield, all players exile all artifacts, enchantments, and historic cards, other than Remnodok, Cryptic Shaper. (Artifacts, Sagas, and Legendaries are historic).
Then, if the optional extra cost was paid, summon
X of the exiled creatures (where 'X' is the mana spent to cast this spell.)