What job in a party does a magus have?

The magus is, ultimately, a fancy fighter. But the differences matter.

For the basics, the magus gains four major class features:

• Spells. One way of thinking about the magus is that the magus uses spells like the fighter uses feats, accepting per-day restrictions in exchange for greater power and much greater variety. This is true, but spells also mean much more than that; see below for more details.

• Spell Combat. This is what allows the magus to do what it does; while the spells are the workhorse of the class, spell combat is the iconic feature that makes a magus a magus. Basically, magi get to two-“weapon” fight, but with the offhand weapon instead being a spell. This means the magus can fight and spellcast simultaneously, which is huge.

• Spellstrike. The magus can turn a touch-attack spell into a weapon-attack spell, combining a attack with the spell effect. This is nice, but not actually all that critical; one additional application of your weapon damage doesn’t matter so much, and a magus should feel comfortable not using this if a non-touch-attack spell is better in a given situation. At early levels, though, using spellstrike on arcane mark (an at-will touch-attack cantrip) can turn spell combat into actual two-weapon fighting, which is sometimes all you really want.

• Arcana. These are various side-benefits that make your magus your magus, different from others. Some of them are quite good, though like most of the “ability off of a list” features, they’re very hit-or-miss.

About fighting and about spellcasting

So on some level, the magus is this fighter who is using magic instead of bonus feats to be better at fighting. But magic is very nearly equal to power in Pathfinder. Being a fighter who uses magic to be better at fighting, rather than a fighter who uses skill and training to be better at fighting, makes you a better fighter, and it makes you a much better adventurer.

Even with a relatively slow spell progression, magi get many, many more spells than a fighter gains feats. That means a magus is much more capable of having answers to a variety of situations—both combat and non-combat. These spells can make the magus fight better than a fighter can (by having more options available), and make the magus far more useful outside of combat.

So the magus’s usual role is that of the fighter, but a fighter who is more versatile, more capable of dealing with the variety of challenges that an adventurer faces, and less forced into a singular niche. Against extremely vanilla opponents (who pose no special challenge to a fighter), the fighter is probably more effective, but especially as more levels are gained, such enemies become rarer and less threatening overall; most real threats do have some special challenge that causes problems for a fighter. Because a fighter can only prepare for so many things, while a magus can prepare for many more things than a fighter can, the magus is more reliably useful, more useful against greater threats, than the fighter is. And outside combat, there is no competition.

A downside: magi multiclass poorly, but then so do most Pathfinder classes

There are some downsides to the magical approach to combat, though: it does kind of lock you into the magus class. You qualify for feats (mostly) independently of class, so if you take a level of fighter at 10th, you can get a 10th-level feat. But you only qualify for better spells (and, though it’s less critical, better arcana) by taking more levels of magus. So if you take a level of magus at 10th level, instead of getting a 4th-level spell as a 10th-level magus would, you get a 1st-level spell. Therefore, magi are not as good at multiclassing. Ultimately, however, Pathfinder punishes multiclassing massively, and the only time it’s really viable is when you can get something particularly potent from a level, maybe two, of a class, delaying some other primary class only a little. The magus class features only work with magus spells, so it is not good for this purpose.

About “role” and how there’s not really any such thing in Pathfinder

Finally, a last point about “role”—Pathfinder doesn’t really have any such concept. Above I’ve described the things that a magus is natively good at, but that isn’t necessarily the same thing. I’ve tried to emphasize, even, that much of what makes the magus better than the fighter is his ability to contribute to non-fighting things. But the fighter’s “role” cannot accurately be described as “damage”—the fighter can be built to do one or two of many things, and a given fighter may not be interested in damage at all, instead focusing on defense or combat maneuvers or intimidation or what have you.

Meanwhile, both cleric and wizard can be built to do far more damage than the fighter can. Clerics, in particular, can be so much more than just healing, being one of the most powerful and well-rounded classes in the game, capable of dealing damage in melee or at range, taking hits, buffing allies, curing debuffs and damage, and even summoning assistance. And by the same token, while “magic” can cover what a wizard does, that term is misleading: “magic” can and does cover just about everything.

So I also recommend that you avoid pigeonholing classes in this manner. Classes have strengths and weaknesses (well, most of them; some of them really seem to lack any real strengths, and others real weaknesses), but they mostly can and should take on many roles—and which roles are as much up to the character, the campaign, and the individual choices made in character creation, than it does to do with the class used.