Here is one version of the standard infantry-based Sylvanian army I believe is competitive.

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Vampire Lord -- lvl 3, additional hand weapon, Aura of Dark Majesty, Ring of the Night, Black Periapt, Scroll

A standard infantry General. You might be tempted to switch the Promotional Pamphlet of Arkhan Inc. for the Aura if you feel you don't need it. 1 Scroll suffices to stop the all-important spells that will lose you the game. Otherwise VC should be soaking up a lot of enemy magic.

Vampire Thrall BSB -- Flayed Hauberk, Wolf Form

You may want to use Sword of Might, but I feel the main thing that differentiates a BD BSB from a vC one is really just Wolf Form, so why not make use of it?

Vampire Thrall -- great weapon, heavy armour, shield, Wolf Form, Summon Wolves

A good all-purpose utility Thrall. Either she joins the BSB in taking out small units or war-machines or mages, or she stays in units providing reliable CR boosts, or she hunts chariots/discourages chariot charging. Summon Wolves is to march-block a flank, fairly important.

20 Levy -- std

20 Levy -- std

20 Militia (FC)

Not much explanation needed for these I think. The Militia are for the General, because they've got the Captain. The rest are just line-holders, that still cause Fear and are ranked infantry. Expect them to reach unit sizes of 30+ for most games.

Bat Swarm x2

Common utility units. If there is nothing good to tarpit, send them hunting gunlines. They still do fly, in a way.

5 Bats

I use 2x3, but competitive lists use 1x5, I've noticed.

5 Wolves

5 Wolves

Ubiquitous. Not much explanation needed.

Spirit Hosts x2

If there was no BSB I don't think I'd even include them anymore. What with the new Wood Elves, it seems everyone and his mother has an answer for Ethereals, so they're no longer the huge threat they once were. Still, useful to tarpit knights, ogres and such, and if nothing else are magic magnets.

6 Black Knights -- champion, barding

A nice tight economical flanking unit. Units of 6 Knights are cool. Cheap as chips, but can't be ignored.

Banshee

I dunno why she's here, half the tournament armies nowadays are Immune to Psychology. If not for the BSB she really wouldn't have a place. But with the BSB she can actually hold her own -- holding an entire unit in place, for example, as long as the unit doesn't generate static CR beyond outnumber. What comes to mind: Kroxigor, Minotaur without std, Ogres without std, heavy cavalry without std or ranks, etc. And each combat phase she'll be screaming at them. Neat.

This looks to be a very strong list to me. Is this one of yours, Derfel, or something you saw and thought was a good army? Also, I have a couple of points to make on the list:

1. Magic defense. I'm a little worried about the lack of spectral attendants, as I think this is vital to the (small) amount magic defense the AOS has. Although I suppose you could use the periapt to store a die every magic phase...still that only gives you 4dd and a scroll, not enough IMO for a slow, infantry based army. I would be tempted to drop the wolf form on the second thrall, and instead make her a constant CR generator in one of the levy units, and give her spectral attendants.

2. I'm a little torn on the BSB. Usefull, I will agree, for the ethereal units, but I still think the good old flayed hauberk-wolf form-great weapon combo is the best and a must for any Von Carstein or AOS army. However, the BSB might end up being worth it, but I'm just not sure.

3. The bat swarms. Never been a fan at all, I think they aren't worth it at all. I'd drop them, using the points to get another base for the spirit host (I think 3 makes them much more effective), and make one of the wolves scouting. This is in my opinion one of the best things about the AOS, and I would be loathe to create a list without at least one scouting unit.

4. Last minor minor gripe: Through (alot) of playtesting, I have found that the great weapon is actually more effective on a count/lord than and addn. hand weapon. Against rank and file there isn't much difference, but when knights or characters enter the fray, the great weapon really comes into its own. A shame to waste that high initiative, though.

This sort of list is actually pretty standard by now, for anyone that still plays infantry-based Sylvanians. The way some people talk nowadays you'd think all Sylvanian armies were nothing but wolves. But our infantry still does fine.

1. You'd have 5, hopefully, and a scroll. That's really enough against most magic. You're not ignoring your mage-hunting I hope, and making life difficult for enemy mages? Because Spectral Attendants, while worth the points, is not effective enough to sacrifice a mobile thrall and a unit of summoned wolves. Those last two are really huge advantages to have, far more than a -1 to cast that sometimes won't even matter the whole game.

2. The BSB is absolutely awesome. It's not just for the ethereal units -- in fact, I think I tried to imply that the ethereal units were there because I happened to have a BSB. The BSB Thrall is superb to take down skirmishers and fast cav. It also makes war-machine hunting a sure thing. And, in a pinch, join a unit of raised Levy for instant CR, or charge into an ailing combat and turn the tide.

3. Scouting Wolves are fine and good, but usually you don't need them, you have M9. Moreover, some games you will not be able to deploy them as Scouts at all. It's nice, but unnecessary.

I think you might underestimate Bat Swarms. They are still Unbreakable, and being able to fly 10" is extremely useful. Being skirmishers means they can do things the Hosts can't. This army was built to be both streamlined and yet able to handle most any threat. Skirmishing Swarms are one of the most annoying counter-units your opponent will have to deal with.

4. Personally I prefer the great weapon also, but many players stick with the additional hand weapon, due to its sheer effectiveness against rank and file. Notably, Saurus Warriors are said to fall fast to a Lord with the extra hand weapon. Possibly because assuming they stick around for the next turn, they're striking last, instead of the Lord striking last. Now I've had my Lord killed by lucky Temple Guard before, so I can appreciate this line of reasoning!

With regards to the bat swarms, I really am not sold on these guys. You make somewhat valid points, but since you already have the spirit hosts and two units of militia, why do you need more tarpitting units? Besides, you can always raise more tarpit units with invocation. These guys really have to purpose to me: if you want more gunline/warmachine hunting get more bats or wolves. These guys, to me, don't fit.

I'm also kind of missing the point of the bsb: why would he be better at mage/warmachine hunting than his great weapon armed counterpart? The great weapon, to me, gives the character much more versitility: the ability to destroy chariots (an ablity not to be taken lightly), better combat capabilities, etc...losing one less zombie/skeleton never really seemd to justify the points to me. Just my two cents.

Valid concerns. I'll try to address them.

The Bat Swarms trump the Spirit Hosts and Levy units in one very important thing, some would say the most important thing in WHFB: movement. Being Skirmishers and Flyers, they can go in directions that none of the other tarpits can. They can go in places where Levy can't go, and where you have no Markers near, and raising units successfully is not guaranteed. They can move in ways Spirit Hosts can't, in all directions.

The BSB is really very simple: a guaranteed point of CR is better than having extra strength against war-machine crew -- honestly why do you need S7 for those? And in case you lose combat, you need to lose by quite a bit to lose the BSB. The s5 is just enough to handle skirmishers and fast cav, and the banner helps you win the combat, or at least stay around, and not strike last in subsequent turns. He is, in fact, far more versatile than his great-weapon counterpart -- which you will notice I have included, because he's great too.

As for destroying chariots... you ever faced 3 Tuskgors before? 3 Cold One Chariots? 4 Tiranoc Chariots? If you have, you will understand that s7 chariot-hunting is not all it's cracked up to be. People are very willing to flee with a chariot if it means tagging your failed-charge Thrall during their turn.

For me the bsb is a major gamble, he's worth so many pts and does he really do enough to merit the risk that is taken with him? Around 300pts if lost for +1 combat res, a bit of extra surivabilty on expendable units and less hitting power. I'd go the 2nd wolf thrall with great weapon or maybe 2 more hosts or a banshee and something, they'd do more for me in a competative army and they'd give you redudancy rather than a points sink which against a good player with a nasty list will be more trying to stay alive and not give 300 victory pts away.