Morale and leadership are the hardest part of alien species in SGII, because we humans don't really have a particularly large dataset of real examples to draw from. So this is where we have to make some assumptions.
Proposition 1: Zerg battle-units are bred for killing. They're hungry. Their instincts tell them to go forth and devour, even without any mental urging from the hive mind.
Proposition 2: The Overmind exerts its influence over the swarm through overlords, giant flying psychic transport whale-bugs (kind of).
Proposition 3: Zerg units of the same genotype do vary to some degree in maturity / quality. Ex: Devouring Ones vs. adrenal zerglings vs. zerglings. All the same breed, more or less, but of varying quality.
These propositions suggest or imply the following:
- A zerg squad's leadership value is a measure of how strong its link to the hive mind is (receptivity, if you will). Note that there is no single 'squad leader' element; leadership measures the reception each individual in the squad gets. As a result, you never lose the squad leader (but you also never get leadership upgrades by replacing poor leaders).
- If a zerg force has a command squad, it's an overlord (which basically operates as a tank-sized VTOL vehicle with EW, transport, and command capabilities).
- Zerg units do have unit qualities just like human units, but based on the quality of their genetics. Hunter-Killers are elite, upgraded grooved-spine hydras are veteran, bog-standard hydras are regular, and perhaps 'rush-job' hydras are green; the Overmind sacrificed quality for rapid growth, resulting in a wide variety of negative mutations which impede performance.
- As a zerg squad's morale deteriorates, they become less cautious and prone to close-assaulting the enemy against orders. When they would be broken, they may turn against their own kind.
Morale is really the only complicated thing there. Below I propose a modification of the Warbard's rules for Kra'Vak morale.
At Confident and Steady, or Calm and Irked, a Zerg squad may take any action normally available to it.
At Shaken, or Mad, a Zerg squad cannot enter cover or retreat from the enemy unless it passes a Reaction test.
At Broken, or Angry, a Zerg squad must spend one of its actions per round advancing towards the nearest enemy unit, and may not go in-position. If fired upon, they automatically become Routed.
At Routed, or Furious, a Zerg squad must spend both of its actions per round either advancing towards or close-assaulting the nearest enemy unit. If they attempt to rally and fail (or are passed an action by a unit up the chain of command, use it to try to rally, and fail), they fall to Berserk.
At Berserk, the squad must spend both of its actions per round either moving towards or close assaulting the nearest other unit, with no regard for side.
When making reaction rolls to initiate a close assault, Zerg units invert the normal modifiers; they take -0 at Confident, -1 at Steady, -3 at Shaken, and automatically make the reaction test at any lower morale level. They do not modify the morale test for defending against close assault; it's an unexpected and scary situation, for the hunter to become the hunted. Note, though, that even if you drive the Zerg from a hilltop when they fail their morale save to hold their ground, they might charge right back at you next turn...
Now I know what some of you are saying... "But the Zerg want to be in close assault! This just makes them do what they were going to do anyways!" As Heavy would say, "Maybe, maybe... but I have yet to meet Zergling that can outrun Bullet." Put your marines on the other side of difficult terrain before enraging the Zerg. Put firebats between your marines and the Zerg before enraging the Zerg. Minefields are wonderful things. If the zerglings want to remain in cover, make 'em mad and make them come to you. Those hydras want to sit at range? Make 'em mad and then they can't. I think it may be workable.
Oh yeah, burrowing and regeneration. Burrowing's easiest - it operates similarly to In-Position. A Zerg ground unit may choose to Burrow as an action. While burrowed, it cannot move or fire any weapons, but it gains a 1-die shift to its range die and its armor die, as if in soft cover. These die shifts stack with bonuses from actual cover. For purposes of spotting hidden burrowed units, a burrowed unit applies a two-die shift to its range roll; see Hidden Units, page 26. A reaction test is required to Burrow successfully; the difficulty of this test is at +0 in reasonably-soft ground (most terrain, but definitely mud and swamp), but at +2 in areas which are more difficult to burrow into, such as concrete or through the root webs of trees (so in woods, inside buildings, on roads, and similar). Moving out of Burrow operates exactly the same way as moving out of In-Position. A unit may not be both Burrowed and In-Position simultaneously; they're mutually-exclusive states.
Regeneration's slightly tougher. On the scales involved in a typical SG2 game, regeneration is completely ridiculous, so I intend to ignore it. If, however, you wanted to apply a +1 bonus to casualty resolution rules in some circumstances to model regeneration and make up for the Zerg's lack of medics, go for it. Alternatively, you could resolve all Zerg casualties immediately, rather than requiring a Reorganize action, but at no bonus. Also, just for shits, the Zerg take the same penalties for leaving behind injured squadmates as injured humans do; those are their pack-brothers, of one mind and one flesh!
And so, without further ado, on to stats!
Zerglings are light / scout infantry (speed 8") with light armor (d6 armor value) and a close combat weapon (+1 die shift in close combat). Simple, but dangerous in numbers and in close. Note also that they're technically inferior to Firebats of the same quality in close assault, because flamers give a two-die shift.
Hydralisks are slow light powered armor units (speed 6", armor d10) armed with a biological equivalent of an advanced assault right (FP2, Imp d10). Powered armor makes sense here, because they're twice the size of a man, and while they don't have specialized close-combat weapons (arguably...), they have raw mass and brute strength, as modeled by PA's melee doubling. Compared to Terran marines, hydras under this conversion are tougher (d10 armor vs d8 for marines) and meaner in melee, but slightly less punchy at range (Imp d10 as opposed to Imp d12 for the Terran gauss rifle), and use twice as much transport space. So the trouble with hydra deployment and use is that, on the one hand, they're pretty strong in melee, and tough enough to probably get there, but on the other hand, they're also all the ranged fire support your zerglings get. Choose wisely.
Overlords are Size 3 vehicles with Armor 2, carrying capacity 8, and command capabilities. Additionally, they carry an enhanced EW suite (3 EW counters per turn, d8 on EW rolls) and Basic ECM (1d6 on rolls against guided missiles and similar). Movement is where things get really tricky. On the one hand, they're probably best modeled as VTOLs like dropships. On the other hand, they're also slow as anything in SC, which causes problems with SG's aeospace rules, namely that an air unit can move to anywhere on the table as a move action. I'm kind of OK with that for overlords as a concession to reality - air transports should probably be reasonably fast, and they're still countered by guided missiles, which have "Anywhere on the table" range as well. The real question is "Why is the overlord hanging out on the table at all?" There's an essential conflict in its two roles of 'dropship' and 'command unit'. I think a compromise position is this - feel free the move the overlord off-table, but you can't activate off-table units, which means you can't use its command capabilities to transfer actions. So you can protect it, but you lose a hefty chunk of the benefit of having one if you do.
Most of the other Zerg units are just too damn big to have in SG... Guardians are artillery support firing medium-caliber shells (4" blasts). Mutalisks might qualify as gunships, but I never did understand how they actually flew... I'm writing them off just like I wrote off wraiths for Terran. Devourers and Scourges, as with Valkyries, just contribute to the Air Defense Environment. Lurkers are an interesting problem... I'm kind of thinking that unburrowed, they're mid-sized vehicles with no weapons, but when burrowed, they radiate a large minefield that doesn't attack friendlies. Call 'em Size 3, Armor 2, walking propulsion with a speed of 8", and they radiate a 6" radius Mixed AP/AV minefield when burrowed. Great for holding a position, and vehicle armor means that you might actually be able to get up near an enemy unit and then burrow. Rather scary, really.
So that leaves us with Queens, Defilers, Ultralisks, and Infested Terrans to deal with. Infested are probably easiest; they're Independent Figures (per page 27) with d8 armor, 6" speed, and the ability to detonate the equivalent of a Command-Detonated Mine (page 56) centered on his own position at any time, after which he is destroyed. To model the effectiveness of Infested against armored targets like buildings and bunkers, we may want to let them apply 1d10 doubled against the armor of buildings and vehicles within the blast.
So we're down to Queens, Defilers, and Ultralisks. Spellcasters and the superheavy tank. The spellcasters I think could be modeled as variant off-board artillery; Dark Swarm, for example, might be a variant artillery shell type that creates a zone of soft cover in a radius about where it lands, Ensnare creates an area of difficult terrain, and Plague could do something interesting like inflict a penalty on casualty resolution rolls for units that were caught in it (or go with the simple solution of "It's a general-purpose artillery barrage, screw the flavor text."). Battlefield control via unusual artillery, basically. So that pulls those guys mostly off the table... Parasite and Spawn Broodling are odd, in that they're single-target... maybe light artillery? Or just leave 'em out... It also just hit me that I left out Science Vessels last post. Off-board EW capabilities with Enhanced sensors, and whatever Plague ends up doing, Irradiate should end up doing something fairly similar.
And the ultralisk. These should pretty much never be on the table, unless it's like the only unit the Zerg have. You want to play the tank game, you're welcome to... but use Dirtside and keep it out of Stargrunt.
So there are the Zerg... thoughts?
(Proposed modifications following playtesting are here; this version is preserved in its original state for reference purposes)