Let's begin assuming you are casting off of a "scroll" in the form of a spell-scar. From the SRD:
The magus can use special scar-based tattoos called spell-scars on his skin to cast or prepare spells, much like scrolls. He can cast a spell from a spell-scar exactly like casting from a scroll; the ink and scars vanish when the spell is cast. The magus can also prepare spells from his spell-scars without expending them, similar to a wizard using the Spell Mastery feat.
The magus does not need to be able to see his spell-scar to use it. A magus has room on his skin for 18 total spell levels of spell-scars, which he can create using the rules for scribing scrolls (although they do not require the Scribe Scroll feat).
In this instance the "scroll" should be able to be used with spell-combat as it leaves your hand free for spell combat and it functions as casting a spell (see the sources cited in the question). I would note that while activating a scroll is a standard action, spell combat works with standard action spells (that being the whole point). Further from an RAI perspective it would be odd for this arcana (being a class feature of the magus) to not function with the primary feature of magi (Spell Combat).
Now let's assume that you are using a more traditional scroll and you can draw it as a swift action via some method (spring-loaded sheaths, being a tiefling, etc) or already have it drawn (because you theoretically could I suppose). Your hand is not precisely "free" but I would argue you can use spell combat anyway because of the existence of the Wand Wielder arcana which reads:
The magus can activate a wand or staff in place of casting a spell when using spell combat.
Two items of note:
- An interpretation of the word "free" in several other answers implies the hand must be empty as opposed to free to cast the spell. This interpretation would render Wand Wielder useless as an arcana and so we can assume that "free to cast the spell" is the correct interpretation, in which case casting off of a scroll should still be fine.
- There is no Scroll Wielder arcana. This is purely an RAI argument but one would assume there would be a Scroll Wielder arcana if scrolls didn't already work with spell combat.
tl;dr You should be able to cast from a scroll using spell combat assuming you didn't need to use a move action to draw it and that the spell is on your magus spell list.
The short answer:
AC 0-5: Human Great Weapon Fighter with the Great Weapon Master feat wielding a Greatsword
AC 6-20: Raging Human Barbarian with the Polearm Master feat wielding a Polearm
AC 21-26: Half-Orc Two-Weapon Fighter
AC 27+: Human Great Weapon Fighter with the Great Weapon Master feat wielding a Greatsword, part II: the GWF returns.
The significantly longer answer is that here are some calculations I did for the options that seemed obvious to me. Interestingly enough, the Barbarian didn't make the top of the list in terms of pure damage, but it did make the top of the list once we added AC into the mix.
You can also add Caltrops to any of these builds (and you can afford a lot of caltrops) to add up to 1 dmg/r.
Other notes:
- The only source material used for this was the PHB, as I do not have access to all of the adventure paths and supplements
- Magic users need not apply: Cantrips are almost universally low-damage, and they never get to benefit from base stats to get those sweet, sweet flat bonus damage numbers. All other spells are too consumable to be considered, so they didn't make it to the number crunching stage.
- Rogues were briefly considered, but sneak attack just isn't reliable enough when you can't count on nearby allies or advantage.
- No cheese! I tried to stick to a purist approach here. There may be strategies that your GM approves like this but most reasonably GMs would ban that kind of build from their tables for being too OP. This list fits nicely within very vanilla RAW and RAI.
- I gave all characters rolls of 18 for their stats, then added any racial strength bonus that applied. Point-buy only allows you to get to 16/17 instead of 19/20, and will lower your dmg/r across the board.
- All damage is given in expected values, done by hand. It's possible I failed my Intelligence(Statistics) check, so if you see something say something
- Humans used are Variant Humans, to take advantage of the bonus feat. Half-Orc is used otherwise as they're the only race I could find that can possibly add damage to their attacks through the Savagery feature, as well as giving a handy +2 Str.
- No magic weapons are used, as they are out of the budget of level 1 characters even if they sell all of their possessions, max out their starting gold rolls, and take the Noble background
- Using the point-buy system the half-orc takes a bigger hit than humans to both his to-hit values and his damage (the +2 doesn't get him to a higher Ability Modifier tier). This results in the Barbarian Polearm Master reigning supreme all the way to 24 AC, and the GWF picks up the slack at 25+, cutting the half-orc out of our equation completely.
- You want numbers? Here's a Google Sheet with some numbers.
Without further ado, here is my list of damage-optimized level 1 characters (please refer to the above sheet for numbers with AC factored in).
Human Great Weapon Fighter with Great Weapon Master feat (22.75 dmg/r, +1 to hit)
- +4 str bonus
- +10 feat bonus (-5 to hit)
- 2d6 (reroll 1,2) greatsword attack (22.333333 dmg/r)
- 5% crit (.41666666 dmg)
- Total damage on maximum Crit: 14+12+12 = 38 dmg
Human Barbarian with Polearm Master feat (20.3 dmg/r, +6 to hit)
- +4 str bonus
- +2 rag bonus
- 1d10 polearm attack (11.5 dmg)
- 1d4 bonus attack (8.5 dmg)
- 5% crit (0.4 dmg)
- Total damage on maximum Crit w/ both attacks: (6 + 10 + 10) + (6 + 4 + 4) = 38 dmg
Half-Orc Two Weapon Fighter (17.4 dmg/r, +7 to hit)
- +5 str bonus
- 1d6 shortsword attack (8.5 dmg)
- 1d6 shortsword attack (8.5 dmg)
- 5% crit including extra damage die from Savagery (0.7 dmg)
- Total damage on maximum Crit w/ both attacks: (5 + 6 + 6 + 6) + (5 + 6 + 6 + 6) = 46
Human Two Weapon Fighter with Dual Wielder feat (17.2 dmg/r, +6 to hit)
- +4 str bonus
- 1d8 longsword attack (8.5 dmg)
- 1d8 longsword attack (8.5 dmg)
- 5% crit (.45 dmg)
- Total damage on maximum Crit w/ both attacks: (4 + 8 + 8) + (4 + 8 + 8) = 40 Dmg
Best Answer
1st place: Spike Growth
Spike Growth creates a 20-foot radius (40-foot diameter) circle which is difficult terrain and causes 2d4 damage per 5 feet of distance that a creature travels through it. Making the assumption that:
Then the spell will deal 24d4 (60) points of damage per round - averaging 600 points over the full minute allowed in your conditions.
You're very unlikely to be able to actually get that performance out of the spell, since it does depend heavily on your enemies making very poor tactical choices, or that you are otherwise able to ensure that they need to keep moving through the affected area - if they stand still or can walk around it, they take no damage.
But, if circumstances are perfect and your foes keep dragging themselves through the thorns, no other second level spell comes close to spike growth's damage. Even if you make the assumption that you only get half the damage out of it and do a total 12d4 (30) damage per round, that's still nearly as good as what you can get out of other optimising other 2nd level spells.
Spike growth is available (at character level 4) to druids, Nature domain clerics and warlocks with the Genie (Dao) patron.
2nd place: Moonbeam
Spike growth's position as number 1 requires a lot of very favourable assumptions about the battlefield and enemy behaviour. An alternative more likely to be viable in practice is moonbeam, which creates a 5-foot radius (10-foot diameter) cylinder that deals 2d10 damage to any creature which starts its turn there or enters it for the first time during a turn.
As per the questions' premise, we'll assume that 2 enemies in any given round will either start their turn in the area or pass through it as a part of their movement during their turns, each taking 2d10 (11) damage for a total of 22 damage dealt per round.
However, that only covers the damage that moonbeam deals on the enemy's turns. If an enemy ends their turn standing outside the area but is moved into or through the area during someone else's turn - i.e. yours - they will take an additional 2d10 damage.
As per the question's premise, we will assume that at least one of the enemies always helpfully positions itself just next to the moonbeam in such a way that, on our own turn, we can push or pull them to force them back into the area. Any caster could achieve that using a shove attack, but a druid could do it more efficiently using the thorn whip or gust cantrips to respectively pull or push the enemy into the area.
Under that assumption, we increase the total damage per round to 6d10 (33) and so deal an average total of 330 damage over the minute that moonbeam lasts.
Above and beyond this, if we're a druid, we also have access to the thunderwave spell, which can be used to push around multiple enemies at a time. If we devote our remaining 6 spell slots (4 1st, 2 2nd, assuming all four levels are in full-casting classes) to casting thunderwave, then on six of those turns we can conceivably force both enemies back into the moonbeam, and so in six of those ten rounds we will actually deal 8d10 (44) damage, and moonbeam's total average damage over the full minute will be 396 points.
(It is important to note that although we can also use an action on our turn to move the moonbeam around, the official interpretation of the rules according to Sage Advice holds that moving the area of moonbeam onto an enemy does not count as the enemy "entering the area", so this cannot be exploited to deal extra damage - to get the extra points out of it, we must rely on forcing the enemies to move, not moving the moonbeam.)
Moonbeam is available (at character level 4) to druids and Twilight domain clerics, but druids have the easiest time maximising its effectiveness by combination with other spells.