Dualcaster Mage | Black Sun's Twilight | Naru Meha, Master Wizard

Cards

Naru Meha in your graveyard.
Dualcaster Mage and
Black Sun's Twilight in hand.
({6} magic symbol) ({B} magic symbol) ({R} magic symbol) ({R} magic symbol) available.

Cast
Black Sun's Twilight by paying ({5} magic symbol) ({B} magic symbol) .
Holding priority, cast
Dualcaster Mage by paying ({1} magic symbol) ({R} magic symbol) ({R} magic symbol) .
When
Dualcaster Mage enters the battlefield, it triggers, copying
Black Sun's Twilight, targeting
Dualcaster Mage.
Resolve the copy of
Black Sun's Twilight, giving
Dualcaster Mage -5/-5 until end of turn and returning
Naru Meha from your graveyard onto the battlefield.
Dualcaster Mage dies as a state-based action due to having less than 0 toughness.
When
Naru Meha enters the battlefield, it triggers, copying
Black Sun's Twilight, targeting
Naru Meha.
Resolve the copy of
Black Sun's Twilight, giving
Naru Meha -5/-5 until end of turn and returning
Dualcaster Mage from your graveyard onto the battlefield.
Naru Meha enters the battlefield and dies as a state-based action due to having less than 0 toughness.
Repeat from step 3.

Since creatures with 0 or less toughness only go to the graveyard as a state-based action after the current spell or ability is finished resolving,
Dualcaster Mage +
Black Sun's Twilight is not a valid combo on its own. The creature must go to the graveyard before the spell starts resolving.