AnotherGuy
Hero
Taking out the boss is a valid strategy.
Intelligent Boss monsters also know this and prepare for it.
So,
The 5 enslaved wizards all cast warding bond on the BBEG giving him +5 to AC and Saving Throws and resistance to everything.
- they are in another room while their Minions fight the Party.
- The BBEG is protected by a force field that is powered by Crystals protected by Quantum Orges, that need to be destroyed first.
- Use a Goblin Boss with redirect attack.
Or just double the HP of the Boss and give him higher AC.
- Separate the party...
Last session the PCs took on Iymrith in her lair, she separated the party by collapsing one of the corridors. I did though have to decrease her Legendary Actions as she was fighting only 1 PC.