Imagine a minotaur mob. He is carrying a giant shield that reflects magic and ranged attacks. It also provides him with very high PRR against melee attacks. While carrying the shield, he is immune to CC, similar to if he was always blocking.
If a player closes distance with him and attempt to flank, he'll perform a spin attack that pushes everyone around him away.
His primary attack, however, is performing a powerful charge attack that ends with him slamming his shield in to the ground at the end of it, causing high damage (instakill if you want) to any player hit by the shield. The charge attack starts with the normal minotaur animation that they perform before charging, so that players have a chance to avoid said attack. If he misses his shield smash, his shield gets lodged in the ground.
For 3 or 4 seconds, he will be attempting to dislodge his shield and will be completely immobile. While his shield is stuck in the ground, he loses its reflective properties (unless attacked from the front).
If players flank the minotaur during this time period, they can attack him from behind, where his shield provides no defenses. If players manage to flank him and hit him without his shield, they can do large amounts of damage to him.
He doesn't have True Seeeing, or See Invisibility. A rogue can also sneak up behind him before he's aware and attempt to assassinate him from behind.