You can play up to one stratagem for each different character, trait, or faction listed on the stratagem, as long as your starting team includes that character, trait, or faction. For example, if your starting team is all Autobots and includes
Optimus Prime - Legendary Warrior, you can play both
Heroic Spotlight and
Duty & Honor.
Stratagems go on the battlefield. At the beginning of the game, as you reveal your team, you also reveal your stratagems.
Some stratagems have an ability that causes them to flip. What does that mean?
[Source: WotC] 
Flipping a stratagem essentially turns its ability off. This happens on one-time abilities to remind you that you've already used them.
Does a stratagem count as a card in my deck of battle cards?
[Source: WotC]
No. Stratagems are never put into your deck.
Yes. Each one counts as one of your ten battle cards in the sideboard.
How should Stratagems be treated when using a W5 pack in Turbo?
[Source: WotC]
Treat it like a regular star card.
When do you choose to add stratagems out of your sideboard? When declaring characters or when sideboarding battlecards?
[Source: Aequitas]
Stratagems are played concurrently with the starting team for a game. This is required otherwise cards like
Master Converter and
Aerial Enhancements would not effect the starting team, leading Windsweeper to be sad when Blitzwing and Tracks don't count as Planes.
Does a stratagem changing the attack/defence of a character change the base values for the character?
[Source: Aequitas]
