Or can I pass without attacking?
Last night I wanted to hang onto my last card (Claw or Reinforce), let my opponent kill my dragon, and Reinforce a new one to the battlefield giving me some new battle cards. We played it that attacking is mandatory, which forced me to burn my Claw or Reinforce card and lose that battle.
Followup question: If I CAN pass without attacking, can I then attack in later turns? Say, after my Reinforce pays off with a new had of battle cards?
Attacking and defending are always optional.