Act Together

to

You and your eidolon act as one. Either you or your eidolon takes an action or activity using the same number of actions as Act Together, and the other takes a single action.

For example, if you spent 2 actions to Act Together, you could cast Breathe Fire (2 actions) and your eidolon could Strike (1 action), or your eidolon could use their Dragon Breath (2 actions) and you could Stride (1 action).