Hellton, Dimir Assassin

You cant spend mana to cast this card.
Delve, Convoke (this can be any color mana)
Whenever a creature leaves the battlefield if it
wasn’t cast from your hand
create a token
copy of it that is an assassin
in addition to its other types.
Whenever an opponent takes 10 or more
damage from assassins
you control mill the top 10 cards of
your library.