The behavior of Sub-Zero Atmosphere can have several consequences that you may not have considered. It affects all villain cards, including the villain character cards. Here are some situations you might encounter that are unusual, but work correctly.

Playing Sub-Zero Atmosphere against Omnitron can be quite dangerous. On Omnitron’s character card, it plays a card at the end of the villain turn (from the trash on one side, from the deck on the other). With Sub-Zero Atmosphere in play, that happens at the start of the villain turn instead. Any end of turn or start of turn effects on the played card will happen immediately, since it’s still the start of the villain turn. This can result in Omnitron playing components that deal damage immediately, or an Electro-Pulse Explosive dealing damage immediately.

Grand Warlord Voss is another opponent where any Sub-Zero Atmosphere usage must be considered carefully. On Advanced, he plays a card at the end of the villain turn. This can result in situations like Forced Deployment being played, being immediately destroyed, putting a lot of minions into play, who all deal damage immediately due to Sub-Zero Atmosphere. Even worse, the TCF Conquerer destroys a hero ongoing card at the start of the villain turn. If that card is Sub-Zero Atmosphere, then any end of turn effects that already happened at the start of the villain turn will happen again at the end of the villain turn.

Similarly, on Citizen Dawn's flip side she plays a card at the end of the villain turn. With Sub-Zero Atmosphere in play.. you get the idea!