Tetrahedron Archea-relic

Mill {x} cards where {x} is the amount of mana
spent on the last two creature you cast combined.
If any cards among these have the hexproof mechanic,
remove it and give them (+x/+x) divided by two,
(if odd, round down).This creature can now be
cast for {x}-3 less mana than its original price.
You gain one life and exile
a random card from your graveyard.
Huh?