While playing Alchemy on PC (Windows 10), My Relentless Lawbreaker was taken from my hand when the opponent played Deep-Cavern Bat. When Deep-Cavern Bat was destroyed, my Relentless Lawbreaker stayed attached to the Deep-Cavern Bat. I could open my opponent's graveyard and still see my card attached and no Relentless Lawbreaker appeared in my hand.