Off the top of my head ...
Sith Triumvirate Raid Nihilus ... Lord Of Hunger ... whenever an enemy damages Nihilus with a Basic attack, he inflicts Defence Down on them for 1 turn. If they already have Defence Down, they lose 25% Protection and Nihilus gains that much Protection.
"Oh well, I'll just pass then."
Suddenly Nihilus loses a lot of his sting.
AAT Raid Grievous ... Tactical Manoeuvring ... very tenth time Grievous takes, Grievous and another random ally gain 100% turn meter and reset their cooldowns.
"Oh well, I'll just pass then."
Suddenly Grievous loses a lot of his sting.
Darth Sion ... Lord Of Pain ... At the end of each turn, Sion inflicts Pain for 3 turns on enemies who damaged him this turn.
"Oh well, I'll just pass then."
Suddenly Sion loses a lot of his sting.
etc.
There are too many effects on this game that are intended to punish you for attacking. Being able to pass would render them all useless.