How do you keep 20th level D&D characters from ruining your entire campaign? Very, very carefully.
One of the biggest attractions of Vecna: Eve of Ruins, the final campaign in the decade-long series of fifth edition Dungeons & Dragons, is the fact that you can play as a high-level character. Most D&D campaigns end around level 10. Eve of the ruins starts there and then progresses to level 20, the game’s limit. That means players start the story with extremely powerful, potentially game-changing spells and abilities. So how did Wizards of the Coast’s designers manage to keep the characters aligned so they couldn’t blow up the entire story from the jump? The answer is very, very carefully.
First of all, the danger here is real. High-level magic users can cast many powerful spells before or at level 10. These can be used to quickly reveal secrets that would spoil things like the true intentions of main characters or the locations of people or objects. Casual use of these skills, especially at first, could actually ruin everything. So designers have explicitly noted that some areas in Vecna: Eve of Ruin are different from others. That includes the general use of Non-detection in certain locations. It’s a spell in the Player’s Handbook that ensures that people and objects “cannot be targeted by anyone fortune telling magical or perceived” by other magical means. Other nerfs are not so subtle.
It seems that the teleportation abilities were a particularly big concern. Vecna: Eve of Ruins does a lot of narrative hand-waving to dilute or completely subvert them. For example, the hub location for the campaign is Sigil, the City of Doors in the Outlands. It’s an entire plane of the multiverse that can only be entered or exited through a series of obscure portals. Once players leave the hub, they cannot return until the job is done.
In other locations, it is simply stated in the “Regional Effects” section of a given chapter that certain spells do not work as intended – including teleportation and summoning spells, and spells that could otherwise reveal the location of a creature or object. you might be looking for.
The biggest nerfs are no nerfs at all. They’re traits baked into the high-level monsters players encounter over the course of the campaign. These include the regular assortment of features we’ve seen for a decade now, like responsiveness that activates when characters gain the upper hand and powerful resistance to certain types of damage. There’s also the all-encompassing ‘legendary resistance’ feature that has been part of this edition from the very beginning. That means for some creatures Vecna: Eve of RuinsIf a character gets them right with a spell or other ability that requires them to make a saving throw and they fail, they can simply choose to succeed.
Smart Dungeon Masters naturally expect these things and draft suggestive in-fiction descriptions rather than simply saying, “No, you didn’t do that!” and read the line aloud.
There have been plenty of times while playing D&D where I’ve saved my butt as a DM because of a special rule that designers have carefully incorporated into the text of the book. After all, that kind of oversight is one of the benefits of running a published adventure. And it shouldn’t come as a surprise to players either. Did you really expect it to be different in a game where the person at the head of the table can hide their roles behind a screen and more or less legally lie to your face to spice up the story?