In Mortal Kombat (aka Mortal Kombat 9, 2011 version) for the PS3 and Xbox 360, you can fight the hidden kombatant Classic Noob Saibot during arcade mode under certain conditions to earn the hidden Brotherhood of Shadow achievement/trophy.
To fight Classic Noob Saibot, wait for him to appear in the background of The Temple stage. Win that battle without blocking at all and you’ll fight him.
Check out my other guide if you’re looking for the other Hidden Kombatants for achievements or trophies.