The new D&D Essentials Kits includes a simplified version of the sidekick rules with the idea that a DM could run a game for one player, and it will work out because they’ll have a sidekick. I’ve been running the included adventure (“Dragon of Icespire Peak”) for my son, and so here are my thoughts on how to make that actually work.
NPC Hit Points
Tweaking the opposition is the easiest dial to turn when adjusting encounter difficulty.
The core D&D rules already reflect the fact that different monsters of the same type can have different HP: that’s why they’re displayed as hit dice, because they have a range. Let’s look at the lowly zombie:
Zombies have an average of 22 Hit Points, but they can range from 12 to 33. For some groups with powerfully-built characters and tactically-minded players, I’ve set monsters to the maximum just so they last long enough to last more than one round.
You can go the other way, too, and for single-player games, I strongly recommend setting monsters to their minimum HP. If that zombie is pumping out 2-7 damage per turn, a level 1 character can easily get taken out in 1-2 rounds, especially if the zombie gets a critical hit. Try to manage that so that the player feels like they have a real chance to succeed. (Also consider having the NPCs do less damage, but be careful not to make the player feel like they aren’t playing “real D&D”.)
As an addendum: consider going the other way for the PC and their sidekicks by allowing them to have the maximum HP for their level.
The new sidekick rules feel a little skeletal to me, but you can beef them up besides just tuning their HP.
If the average party consists of 4 full player characters, and you actually have only 1, give them a little more backup and provide two sidekicks. As the DM, you might have a little more work to do early on if the player doesn’t have much experience. However, sidekicks and NPCs have reduced complexity, and once the player can handle running the sidekick on their own, adding one more doesn’t increase their cognitive load much but it greatly increases their survivability.
By the way, assuming you’re playing in “Dragon of Icespire Peak”, don’t feel restricted to assign those sidekicks the roles the adventure provides. Maybe somebody listed as an “Expert” could be a “Warrior”, for example. If they make friends with an NPC in the adventure, let them recruit the NPC! You can use the rules to turn that NPC into a sidekick and make the world feel more alive. Use this sparingly so the player doesn’t feel like they need to build an army, of course.
Depending on the player’s experience level, you might also let the sidekicks suggest courses of action the player might not have realized are feasible, or remind them of common tropes. The sidekicks should always take a secondary role, of course, and not try to lead the “group”, but think of this like the “hint” button in a video game.
Playing one-on-one D&D is a very different experience and I have enjoyed this intimate type of game tremendously. While I’ve tried giving my son “sidekick” characters in the past, the new rules work better. They need a bit more oomph, I think, but with these tweaks, hopefully you can make this play style work.