Trial of Solidarity’s triggered ability affects only creatures you control at the time it resolves. It won’t affect creatures that come under your control later in the turn.

If an effect allows you to exert a creature as it attacks, you may do so even if it has vigilance. It won’t be tapped.

Each Trial has an ability to return to your hand when a Cartouche enters the battlefield under your control. The Trial is returned to its owner’s hand only if it’s on the battlefield as the ability resolves.