RPGMemes

There's still going to be all the standard lair actions, legendary actions, etc.

I think the best is when you're exposed to mechanics one at a time, acolytes with one aspect of the BBEG's power, some creature with another, a foot soldier with a surprisingly formidable weapon, etc. Then, the finale combines them all. That way the experience is novel and challenging, but the players aren't blindsided when it matters.