In Princes of the Apocalypse Ch. 6,
Oreioth, the necromancer and self-styled Lord of Lance Rock
has plenty of time and warning to prepare for his encounter with the party, along with the spells to do so:
Mage Armor and False Life at 3rd-level.
He is also in possession of a powerful magic item,
a Wand of Magic Missiles,
Which the adventure says he grabs before combat breaks out. He’s also alone, cornered, and clearly has no qualms about such evils as murder.
Furthermore, his stat block gives him the special ability to
Cast Animate Dead as a single action as long as he’s just killed someone.
Because he's alone with the PCs, this special ability can only practically be used on a PC.
Finally, the adventure explicitly states that the dungeon in which he appears should be handled while the characters are 1st-level, and the book states the whole campaign is designed for four PCs.
All of these things together seem to imply the designer’s intent is to have him use all (or all but one) charges of the magic item to instantly kill a PC and then use that special ability on his next turn.
However, my understanding of encounter design according to the Dungeon Master’s Guide is that this encounter would be Deadly without the magic item. After adding in the magic item’s ability to cause instant death and the fact that his special ability tips the action economy in his favor, the risk of a TPK rises greatly.
I’m second-guessing whether I’ve understood the intent of the designers here. Is this campaign really designed to make the instant death of a PC in the first dungeon a likelihood of the party ignored his repeated warnings to flee?