Sub-Zero Atmosphere causes villain cards which would act at the end of the villain turn to instead act at the start of the villain turn.
Omnitron flips at the start of his turn and does something different on the end of his turn depending on which side he’s on.
We decided that with Sub-Zero Atmosphere in play, then at the start of Omnitron’s turn we had a choice as to the order of him flipping vs getting a villain card, so we chose to have him flip first. Then, having flipped, the normal end of turn action of getting a villain card from his other side became a start of turn action and got triggered. I figure that if we’d done things in the other order, we would have needlessly been causing Omnitron’s normal end of turn action from BOTH SIDES of his card every turn.
Omnitron’s start of turn is always listed first on the card, and his end of turn is always listed last on his card. Sub-Zero Atmosphere reassigns end of turn actions as start of turn actions. There is still an order listed on the card, such that the first one listed occurs first. Thus, as the flip action is stated on the card before the obtain villain card is listed, Omnitron will flip before any other action listed has a chance to act.