The Omega keyword creates a lasting effect that states, “The active player cannot play, use, or discard any more cards for the remainder of the current step of the turn sequence except through the resolution of pending abilities and effects.”
When playing a card with Omega, this lasting effect is created as the card enters play (for artifacts, creatures, and upgrades), or immediately after the card is revealed (for action cards). If a card would gain omega as it enters play, the lasting effect is created as the card being played enters play.
Once the pending abilities and effects have completed their resolution, play continues to the next step of the turn sequence. If the card with Omega leaves play during the resolution of the abilities and effects, the current step of the turn sequence still ends when resolution is complete.
Rulings
The resolution of Autocannon’s ability in the “after a card is played” window will result in Duskwitch being destroyed, but the lasting effect from Omega is already established and the step will still end once pending abilities and effects complete their resolution.
The resolution of Autocannon’s ability in the “after a card is played” window will result in Duskwitch being destroyed, but the lasting effect from Omega is already established and the step will still end once pending abilities and effects complete their resolution.