So Major Shockwave's ability where he can play Decepticon cards or secret actions on the top of the player's deck as though they were in the player's hand, does this mean at any time since his other ability allows the player to look at the top of their deck at any time? So during attacks or while defending, and during my opponents turn can I play these cards as long as they're on the top of my deck? Or do these actions and upgrades count as the action and upgrade for the turn? And finally, can it only be done once a turn, or any number of times if I have three or so of those cards in a row on top of my deck?

Major Shockwaves ability doesnt change when you can play any card. If you play an action from the top of your deck this way, that is your one action for that turn. If another effect allows you to play additional actions, you can keep playing them from the top of your deck, if applicable.

Source: Wizards of the Coast (2019-07-29)    【Link to Ruling】

Tags: Major Shockwave, Applied Sciences • Scientist