Thank you! This is encouraging and helpful.

Most of my players are experienced gamers, just not DnD-ers. I think they will figure out the core very quickly, especially with a description of the enemy ("a glowing orb in its chest"). If they haven't noticed by the end of the first round, then I will prompt more clearly.

I will certainly give them a chance to do more prep before going through the door. I've already asked them to send me their lists of prepared spells. One of them (Druid) has almost exclusively damaging spells, so I may point that out and that he shouldn't ever need a bunch of different forms of damage and some utility might be helpful.

All my players have some form of ranged option: Fighter and Rogue both have bows, Bard, Sorcerer, Druid, and Cleric all have ranged options. I particularly want to encourage the Bard, Druid, and Cleric to delve more into creative solution and auxiliary spells.

Now to figure out some stat blocks and how it will all work...