The Seraphim have a unique mixture of unit types that seem to combine the military philosophies of some of the other factions. Like the UEF, the Seraphim have higher armor ratings (the second-highest on average) when comparing their units to their counterparts in other factions. The Seraphim also share the Cybran's proclivity for high ROF and moderate-to-low DPS when it comes to some of their weaponry (most notably the Seraphim T2 Assault Bot known as the Ilshavoh and the Seraphim T2 Point Defense). As a result, they combine strong defenses with accurate & consistent firepower, making for a formidable faction.
The Seraphim are most notable for their units versatility. Although they have fewer unit types in comparison to the other factions, their units are more capable of taking on a variety of tasks. Examples include the Seraphim T1 Combat Scout, which is a combination of the T1 land scout and T1 light assault bot; the Seraphim T3 Battleship, a combination of the battleship and T3 strategic missile submarine; and the Seraphim T3 Siege Tank, which is a rough mix between the T3 armored assault bot and T3 heavy/siege bot.
Conversely, some of the Seraphim units need complementary units to support and cover weaknesses, much like the Aeon faction. A notable example is using Seraphim T2 Cruisers to support Seraphim T2 Destroyers due to the destroyers' lack of anti-air abilities. The Seraphim T3 Strategic Bomber also lacks anti-air defenses, much like the Aeon version.
Their experimentals are also quite formidable. The Seraphim Experimental Assault Bot can handle both ground and air units with relative ease, and the Seraphim Experimental Missile Launcher is considered a game ender. The Seraphim Experimental Bomber is expensive and time-consuming to construct, but is extremely effective and fast for an experimental unit. (It is perhaps due to their effectiveness that the Seraphim experimentals are fewer in number when compared to the other factions)
The Seraphim Armored Command Unit has perhaps the most combat potential of any of the factions' ACU's. Although it lacks the sheer offensive ability of the Cybran Armored Command Unit, the Seraphim ACU can be upgraded to do 400 DPS (or even 800 DPS) with speed enhancements and area of effect damage. The addition of enhanced nano-repair packs means that the Seraphim Armored Command Unit can potentially have more than 56000 HP (with sufficient veterancy), and with the enhanced healing rate, the Seraphim ACU can act as an experimental unit. Early game-expansion and defense can be made easier with an upgraded Seraphim ACU to deal with waves of T1 units, and particularly skilled or daring Seraphim commanders can use the uprgaded ACU to assassinate the enemy ACU directly.
On the ground, the Seraphim carry the advantage with their Seraphim T2 Assault Bot, which combines strong defense with very consistent firepower - a must when handling large numbers of T1 units/structures. Using a Seraphim T3 Mobile Shield Generator to provide defense increases the survivability of the ground forces even moreso than the inferior T2 mobile shield generator used by the Aeon and the UEF. The effectiveness of the assault bots extend even into the T3 levels, and smart Seraphim commanders will make liberal use of them throughout the battle. As the saying goes, "A Seraphim player without Ilshavohs is a Seraphim player who is probably losing."
The Seraphim's lack of effective T3 gunships means that a Seraphim commander will need to rely on large numbers of Seraphim T2 Gunships with air escorts, or stick with Seraphim T3 Strategic Bombers with air escorts as well. In addition, the Seraphim anti-air weapons lack any sort of tracking abilities, making the Seraphim ill-suited for using anything but air-superiority fighters and T2 mobile anti-air vessels for taking out air units.
In terms of naval combat, the Seraphim can effectively secure naval supremacy with a combination of Seraphim T3 Submarine Hunters and Seraphim T2 Cruisers. The Seraphim T2 Destroyer can act as a support unit for the cruisers and also submerge if necessary, further adding to the Seraphim's naval potency. While the Seraphim vessels do not have as high of DPS as the Aeon, their ROF generally rivals if not surpasses that of the Cybrans. In addition, the versatility of their naval vessels means that a diverse naval fleet is not necessary to secure naval supremacy.
Effective strategies Edit
I find the Seraphim have the best T3 push. If you combine even a few siege tanks with one or two mobile shields, you will usually win. this works even better if they are supported by sniper bots.
Ythota's are trash on defense due to their death lighting. However it is often beneficial if not necessary to walk a ythota into another base. You might think that sacrifing an experimental is not the best thing to do, but remember. The enemy does not have a base anymore. Even if there is an expiremental in your base, then you can have a base trade. Plus, a ythota can't beat a colossus or a well microed monkey lord, so it's better to just do as much damage as possible.
The Seraphim have no obvious weaknesses, with their land and naval units being excellent, and their air units being adequate. But they lack a clearly defined general strategy that most players use, making them exciting to watch for SvS dogfights, but not so useful for planning the game out in the long term.
The Seraphim ACU has immense regeneration capabilities when fully upgraded, allowing it to pull units back from the mouth of robot hell. The Seraphim ACU is arguably the best out of all the factions' ACUs. And the Seraphim shields are better than any other in all-round survivability. If you know how to exploit these advantages, these vengeful aliens seem to be breaking the game balance in a big way.
Or are they?
First of all, they are more likely to fail in the air game, because their air-to-ground arsenal is limited(only one type of gunship), their other units are average, they have half-decent anti-air guns, and they lack a unique air unit that has the potential to be a game changer(Aeon Guided Missile, for example). Their air to ground capabilities are frankly pathetic until an Experimental Bomber turns up.
The Ilshavoh-Othuum combo is mighty indeed, but without a Fatboy or Megalith equivalent, what's there to offer your mighty army fire support? Fancy T3 Mobile Shields are all well and good, but what are they against two Fatboys and a ton of Ravagers?
As a last word of warning, it is tempting, especially vs UEF commanders, to go for some sort of Ythotha spam, producing a steady trickle to deal with incoming Fatboys and Percivals, but don't do it. You will get steadily pushed back as the Fatboys pick the experimental bots off at long range. It's best to dump your mass into an Ahwassa or a standard nuke launcher to make a big hole in the enemy base, potentially ending the Fatboy problem.