Sacrifice: Pyro Mission 1
Pyro's standard statline is pretty straightforward: his units have 80% of normal health, but in exchange they generally hit much harder (It's not unusual to hit 75% harder than their counterparts) and some of them set enemies on fire, doing damage over time that ignores resistances. Pyro is also unusual in that he doesn't have any units who deviate from his stock modifier.
As for the spells he provides at level 1...
300 Mana, 1 Soul
The Cog is Pyro's basic melee unit, and it's tied with the Trogg for best ability to stay relevant as the game progresses. Its special quirk is that when it dies it does damage to units in an area around it -the damage isn't huge, but the splash radius is larger than you might think and the overall result is that a small mob of Cogs can be used to, for example, successfully attack and wipe out a group of artillery units. Where other basic melee would just get killed, the Cogs will take their enemies with them. Cogs also give Pyro a significant advantage when it comes to basic units being used en mass -past a certain point, Cogs will just automatically beat any number of enemy melee unit simply because of the death effect.
Outside their on-death steam explosion, Cogs are fairly average for a Pyro unit. In early missions, Scythes will actually tend to serve you better (Their average damage isn't that much worse, and thanks to leeching they'll usually be tougher in real terms), and in the long haul Cogs are still going to be relegated to specialist roles.
As usual with basic melee, they're slightly resistant to ranged attacks, but you're not going to notice that in real play.
300 Mana, 1 Soul
Flame Minions are, in my opinion, the overall best of the basic ranged units. All basic ranged units rapidly hit the point where they die basically instantly, at which point the Flame Minion's low HP doesn't hurt it in any meaningful way, whereas its superior ability to dish out damage lets it stay usable in situations other basic ranged units are difficult to justify using. They also come with a 'run away' special ability, which lets them self-cast Speed Up, only they run even faster than casting Speed Up on them would result in. This can be useful for chasing down a fleeing wizard or other unit, or if you're willing to do some minimap micromanagement can potentially be used to perform a raid, and of course the usage in the name can be helpful too, particularly if your wizard gets assassinated unexpectedly.
In the long haul, Flame Minions largely stop being relevant, but that's just the fate of most level 1 units so whatever. They have more ability to stay relevant as a source of damage than the other basic ranged units.
As usual, Flame Minions are painfully vulnerable to melee attacks. (x4) Run Away means that if you're insanely good at micro you can minimize the relevance of this, but Sacrifice has so many things demanding your micro it's generally not realistic to pull off that kind of thing.
300 Mana, 1 Soul
Spitfires are basically Gargoyles, only they're not slow but they're only about 2/3rds as tough. Also, they hit harder.
Like Cogs, Spitfires are very effective at clearing out arbitrarily large numbers of low-quality units once you hit a critical mass. Unlike Cogs, they don't have to die to make it work, so I tend to prefer Spitfire mobs to Cog mobs in most situations. They fall away in relevance fairly quickly as individual unit durability goes up, but in the early game they're one of the best units overall, especially if soul counts are high -a large mob of Spitfires is not meaningfully countered by an equivalent number of ranged units.
Overall, I feel Pyro has the best set of basic units, particularly since they all share the point that Pyro's stat trends are overall advantageous once you hit the phase of the game where level 1 units tend to die instantly regardless. For a rainbow build, if I don't specifically want Troggs or the anti-wizard fliers, I tend to default to Pyro.
The Fireball is one of the two best overall basic attacking spells, which is another reason why I feel Pyro makes for a very solid level 1 choice. It hits hard, it travels reasonably quickly, it has a slightly larger splash radius than all the other basic attack spells, and its only particularly significant disadvantage is that it has friendly fire, unlike the other basic attacking spells. It technically shares with Rock the unusually high potential to impact with inappropriate targets, but unlike Rock its physical behavior means it'll almost always hit enemy units if you're not outright flinging it into a chaotic melee.
This does hurt its long-haul utility since it's slightly erratic at sniping Sac Doctors, but in the early game Fireball gives a Pyro wizard a significant edge, particularly when it comes to dealing with basic flier swarms. And in the late game it's one of the better basic attacking spells for taking swipes at melee fliers and heavy melee.
On a conceptual note, it's interesting to me that the manual description and the visuals agree on Fireball being a rock that you're heating up and throwing, rather than the usual mystical orb of fire attached to nothing in particular. It's especially interesting when you consider that the manual places James and Pyro as traditional allies, and that they have a fairly high number of units that are meant to be related to each other's; the Flame Minion is supposed to be derived from Earthflings that joined up with Pyro ages ago, for example.
The mission itself is, uuuuuh, sloppily designed. There's that ambush that's really poorly designed -I wasn't trying to break it to show off that it can be broken, either, I honestly didn't know it could be broken until this recording- and the game does a pretty iffy job of communicating stuff to you. The Boon is also one of those irritating 'how are you supposed to discover this on your own' Boons, in that the objective is to kill everything Persephone-aligned before you take out the tree, including non-hostile forces like those two Peasants near the beginning. (This Boon being why I bothered to go after the ambush at all)
Also notice that we got a chance at the end of the mission to jump ship. Right in the very first Pyro mission. This is part of a broader what-the-heck aspect of how Pyro is handled I'll be covering in more detail, but for the moment I'm going to note that I found this incredibly jarring the first time I ran into it, and I find it jarring every time I'm reminded of it. This is the only time in the entirety of the campaign Eldred will ever be suggested to possibly care about things like 'sacredness' on their own merit, and it's just bizarre how the campaign wasn't anywhere near as aggressive about 'hey are you having second thoughts?' with the literal god of slaughter than with the industrial fire god.
It's especially odd since this is too early for it to matter mechanically. You can absolutely do Pyro 1, betray Pyro for Persephone, and immediately turn around and do Pyro 2, for example. Most of the time when the game gives you an opportunity to jump ship in the middle of a mission, it's far enough along into the campaign that the decision has an irrevocable effect, such as the James-route option to betray James for Pyro in the prototype Pyrodraulic Dynamo mission. For that matter, you can not betray Pyro and still turn right around and do Persephone 2 -burning the Daven Forest to the ground hasn't caused her to refuse to offer a mission, as you can see in the video. So mechanically, even if you want to turn on Pyro, what you should actually do is slaughter everything on the map for the Boon and then just not take Pyro missions after this.
On a different note, we ran into Faestus! Persephone-style Faestus, with the proper skin and everything. He's not joining us permanently just yet, in spite of what you might expect, though he helps trivialize an already-easy mission. Keeping him alive isn't much of a challenge, either, so long as you don't let Druids gang up on him... which isn't much of a concern, given how few Druids are on the map.
Narratively, we get to see that Pyro is... surprisingly reasonable in how he approaches his Bad Guy Behavior. Flee or be killed is a lot nicer than the 'join me or die' that is more typical of villains, and given both routes I've shown off pretty clearly treat Pyro as a bad guy you'd expect him to be much more blatantly handled as overtly villainous. It's especially jarring in conjunction with the game giving you the opportunity to promptly bail on Pyro, clearly expecting the player to agree that Pyro's actions here are especially dastardly. Keep in mind that Persephone and James are perfectly willing to wage war on the other gods down the line, and this includes taking territory and forcing the local inhabitants to convert, flee, or die. It's not shown off in explicit detail, but it's absolutely a thing. Pretending that Pyro doing so to the Daven Forest is awful but Persephone and James doing so to anonymous Pyro/Charnel/etc territory is totes fine is a fairly ridiculous double-standard.
The only thing that's actually of note here is that Pyro appears to be the initiator here, but the opening of the game made it extremely clear that Persephone and Pyro have a longstanding feud. In that kind of situation such perceptions are not actually clear: is Pyro an aggressor without provocation, or is this really retaliation for Persephone 'purifying' a Pyro territory last week, where 'purifying' meant killing everything that moved and didn't swear itself to her? This particularly stands out if you bothered to read the manual, as it talks some about the backstory of the world and makes it clear that this situation is not so straightforward. Especially memorable is a reference to a 'War of Purification' that Stratos characterizes as 'the war of Persephone's tantrum'.
So... seriously, why is the game acting like Pyro's actions here are objectively super-bad?
On a different note, you might remember the exchange between James and Pyro in the first Charnel video going
James: "But you have no followers in Daven, Pyro!"
Pyro: "I can fix that!"
Turns out he was serious, huh?
See you next Pyro mission.