Fallout and Fallout 2Edit
Companions cannot be controlled directly. Instead, one can change some settings for their AI. In Fallout, the controls are rudimentary at best while Fallout 2 is a substantial improvement.
Companions don't level up by gaining experience as the protagonist does.
In Fallout, companions do not level up at all.
In Fallout 2, each companion has a fixed number (typically, 4-6) of predefined levels called "stages" in the form of multiple alternative models for them with different statistics. Each time the player character gains a level, every current companion has a chance to go up a stage i.e. change to a more powerful model. A companion starts with a base model, then advances to stage 1, 2 etc.
Using fixed models also means that a companion cannot permanently gain stats in any other way, e.g. by reading skill books.
Due to a design bug, companions who have 6 stages cannot ever reach Stage 6. That's because the developer who was programing the party.txt load apparently thought that Stage 1 was the initial model and only allocated 5 slots for additional model data. This confusion is visible in Fallout Bible 4 where Chris Avellone only shows the stats for stage models and misses the base model.
The kinds of weapons a companion can use is not determined by the weapon's type but rather by the in-game model the weapon utilizes when used. A companion can use weapons that their character model has animation sprites for. The types of weapon models are:
- Unarmed weapons
- Knife (incl. blades)
- Large rifle (incl. flamer)
- Gatling gun
- Rocket launcher
It's due to this mechanic that a companion's model doesn't change from wearing different types of armor; changing the model would change their qualifications as well. The added benefit here is making it easier to distinguish the companion from regular NPCs wearing the same type of armor.
In Fallout 2, if a companion has a higher active tag skill than the Chosen One, whenever they use that skill on something, the companion lends them a hand by running in and using the corresponding skill on the object themselves. This way, a skill check will be done against their skill level, which allows the Chosen One to do things they would otherwise be not qualified to.
This doesn't, however, extend to other interactions like skill checks in normal dialogue and during regular object use (e.g. it's not possible to use a strong companion to open jammed doors in Vault 8), or when using items that act the same as an active skill (e.g. a doctor's bag). This severely limits companions' usefulness as specialists, as they can't really save the protagonist from having to train all the needed skills and stats themselves.