play that...
You have a battlebox. That is a good jackstarter. Denegra and the rippers are very usefull. I also use the defiler, but that is only because I have no nightwretch to use... The slayer has won me a few games, but a nightmare is a lot better for only a few points more. (Still, the slayer works in the list on a limb...)
The mechanithralls are good at what they do, cheap fodder that can hit heavy jacks hard. With a few debuffs of denegra *(her specialty) they can hit most things with ease and tear it appart. Mine have destroyed Khador jacks in a turn (they had a debuf of denegra on them).
The biles are great because they are cheap and autohit if they purge. most 1 wound warriors wil die from the explosion or the poison afterwards. They are a great threat the opponent will want to avoid. That alone makes them worthwile. They are not really about synergie, although debuffing a target cleans them out even better. And a deathrage on the leader will keep it alive a turn longer when needed.
Pistolwraiths work well on their own, and can also benefit from debuffs. They can hit most things on their own. do 2 hits and the chainattack kicks in. That will prevent a model from moving or combating. (combine with scourge for a model that can't do anything for a turn)
all in all you have a descent list for only 468 points (full units of biles and mechs). add in a skarlock and you have a very descent army. Take a few smaller units (8 each and take another pistolwraith. Take only 6 bile thralls and 8 mechanithralls and take a brutethrall
UA for the mechs. That is a very nice 500 point list... (have to use it myself tonight
most off the info her is from what I gathered on the formums and battle college. I have tried all the units though and was satisfied with how they ran. Use them, you will like it...