Necron Deathmark from your graveyard to the battlefield with
Out of the Tombs instead of drawing a card.
When
Necron Deathmark enters the battlefield, it and
Canoptek Spyder trigger.
Resolve
Necron Deathmark's ability, destroying itself and causing target player to mill three cards.
Repeat from step 4.
Notes
You can pull off this combo in the Necron Dynasties Warhammer 40K preconstructed Commander deck, if you mill your entire library the hard way instead of using
Leveler. In that version of this combo, you do not need to draw any cards beside
Out of the Tombs, as you can begin by returning Triarch Praetorian, which then returns the two creature combo pieces.