Cast Nameless Inversion from your graveyard, as it is a Knight card, by paying ({0} magic symbol) due to Helm of Awakening and Morophon, giving a creature +3/-3 until end of turn.
If the creature has toughness 0 or less, the creature dies as a state-based action.
Repeat as desired.
Results
Reduce any number of target creatures' toughness to zero.
Reduce any creature's toughness to zero when it enters the battlefield.