So...I see the monsters cards...and he plays something else.

Just starting out in the game. Fighting a Goblin Hulk. His trait is to reveal his hand.
He had 2 movement cards and 2 attack cards.
He then played 3 attack cards in a row.
Which is pretty confusing. Is there a hidden card location? The hidden card in this case one-shotted my fighter

 

Probably the card that replaced Obvious Maneuver was an unrevealed attack.

 

The card in question is Obvious Maneuver, which is a trait. When trait is played it gets replaced by a new card drawn from the deck. That newly drawn card is not revealed and in your case was your destiny.