FYI, never take encounter design advice from me: my plan for the next campaign I'm going to run is
- In session 0, give them a one-time-use wand that can, with no saving throw, paralyze a single enemy target for 24 hours,
- Tell them that they should save it for a powerful "End Boss" wizard that they need to apprehend alive
- Throw a suddenly way-too-difficult fight against a different wizard halfway to the "End Boss"
- And reveal that the "End Boss" was actually dead the whole time.
In the best cast scenario, I psyche out the players into using the wand before they think they need to and…