I have run companions in both group games and solo games and, by and large, it's worked out. In LARPs they were simply additional NPCs to deal with rather than true companions so I won't worry about that in this article. I'll focus on my tabletop examples.
First of all, there's Dallas from the Dystopic Campaign. He's a Darkling with Contracts of Darkness who hangs around the PCs' bookstore and gives them occasional advice, jokes, and encouragement during the planning stages of their missions. When I play him as such I take care that his advice isn't better than anyone else's. Sometimes he might step in with an important piece the others have overlooked but only if he were already aware of it and only when the lack of that piece of information would derail the game or unnecessarily frustrate the PCs.
When he gets the spotlight its always reflected spotlight - a chance for the PCs to shine through their interactions with him the same way they can shine when seducing a woman or intimidating a thug. When he's involved in missions it's always in a support role - such as guiding them through the tunnels beneath Miami. When he gets himself involved in combat (which is rare), he's generally in the background until he sees an opportunity and when he acts he has to make rolls just like the PCs do.
It's so easy for a companion to venture into Die-Die-Stupid-NPC territory when the Storyteller doesn't roll for them. Sure that failure on their part might destroy that cool image you had or mean that the PCs won't know that the NPC can do a particular something but think of it this way. How often have you let the dice spoil your players' ideas of how a situation could go down? They've had really cool ideas that weren't carrie don the dice. Suck it up. They do. Naturally this piece of advice doesn't count if you play mostly diceless. Just be sure that similar rules apply to companions as they do to PCs.
Except ... never let a companion steal a PC's kill. They can help. They can whittle away the enemy's health levels. Heck, they can even do an outrageously powerful attack and make a critical hit but you must always lie and tell the players that the enemy still has a few hit points left. Trust me. This isn't a big deal with minor secondary characters but it does matter if the PCs have put effort into tracking down or attacking the enemy.
Beware giving your NPC companion cool abilities. Especially if they are cooler than the PCs. If they are cooler than have them be Yet-Another-NPC. Companions are best played as sidekicks or perhaps as support who are best in domains that the PCs don't cover.
What if you have a really cool idea for a powerful NPC Companion more potent than the Player Character? Can't that ever be done? It works well in movies.
Sure, but you must abide by a few rules:
- Accept that it might not work. If it doesn't work, quickly turn them into plot. They're an enemy in disguise. They've only got 48 hours to live. The players never need know it could have turned out differently.
- The NPC's epic moments must be few and far between. Depending on how epic they are this could be once ever dozen sessions or so (epic sleuth!) or once during the campaign (epic instant kill!).
- The NPC must be liked by the players - not just by you. This means flaws, foibles, predictable strengths and weaknesses, and the ability to need the PCs.
- Let me underline that point: The players must feel that the NPC needs them more than they need the NPC.
- The NPC is never the protagonist. They are always in a supporting role.
- Ideally their powers come with massive sacrifices or at the behest of the player (kinda like a player-controlled canon). If the latter is true, best let the player roll the dice.
- The NPC can only be epic in very restricted and limited ways. Everybody has their niche.
- The players are cool with it.
- The NPC's epic moments feel more like plot. An NPC who can psychokinetically clear rubble out the way or auto-unlocks doors and copes with traps is fine ... if the PCs aren't interesting in traps, locks or climbing as really the NPC is just a plotted workaround for an issue. This still only works if the players like the NPC - otherwise just be rid of the traps.
- Be prepared to remove the NPC. What starts off as interesting might get irritating. Be prepared to remove them. If you don't want to lose access to the NPC, write fanfiction. I don't mean that meanly. I've had NPCs so awesome that they were actually worth writing stories about rather than putting them in a roleplaying game.
- You can generally gauge the interest of the players in the character by legitimately threatening to kill the NPC off or otherwise remove them from the game. The more sluggishly the players react (even if their PCs seem motivated) and the more joking around they do about the NPC dying, the more likely it is time to retire the NPC. I can't stress that enough. If the PCs should be motivated but the players aren't, don't penalise them by making the NPC's death "their fault". NPCs die all the time. Why not just have the boss kill the NPC the moment the PCs enter the room? If the tension skyrockets at the very idea that the NPC might be taken away from them and the players are very motivated then you should feel really, REALLY proud.
This means that when I do unleash it (to signify the end of one campaign and the start of another) it'll be more meaningful and thus more forgivable. Walsh won't ever outshine James Tyler - he will simply galvanise or motivate him. Walsh won't discover awesome powers and then start solving plots with them. He'll discover awesome powers and BECOME the plot temporarily before disappearing for a few years.
My player loves and adores Peter Walsh and his own characters' interactions with him. I know this for a fact because I have an antsy feeling that removing him for an entire sub-campaign is likely to cause him angst unless I work it very carefully and cautiously. Luckily Peter Walsh is a shapeshifter so my player will likely assume that one of his new NPC companions is, in fact, Peter Walsh. This may or may not be true.