Chiron423

Zendikar fetch lands. Arid Mesa, Misty Rainforest, Verdant Catacombs, etc. I now realize you aren't running tricolor, so fetches aren't THAT necessary, but it's good deck thinning.

Door of Destinies is bad for Slivers. There are much better ways to spend your turn 4.

Elixir of Immortality doesn't do anything for Slivers since you won't be dredging yourself.

Galerider and Syphon are not good. Splashing a color solely for lifelink and flying is not a smart decision.

Add in Thorncaster Sliver to get a win condition, either by popping creatures or dealing 20 damage before blocks.

As for other cards, wait to see what Theros brings for Slivers. After that, you can consider changing from Naya to including blue and black again.

Transguild Promenade is really bad mana-fixing since you usually give up an entire turn 2 for it.

With all of the mana-fixing you have (Manaweft, Grotto, Lantern), you don't even need swamps in this deck since you literally only need black for Syphon Sliver. Adding in 2 Forests, 2 Plains, and an Island would help you a lot more than those swamps would.

Legion's Initiative costs RW, acts as a lord for most of the creatures in the deck, and makes you invulnerable to Supreme Verdict and Terminus.

Switch out Psychic Strike for Remand.

I know Remand is $12, but it's worth it when you aren't scrambling for 2 colors to play a counterspell.

And on that note, Watery Grave and fetches if you're playing in Modern.

Needs more Legion's Initiative.

Add in Urborg. You can have a turn 2 20/20.

I've made a similar deck to this, however instead of it being BWG, it's Jund. Blasphemous Act helps so much. In BWG, there aren't many board wipes, so you might want to consider splashing in either Blue or Red so you can get Supreme Verdict or Blasphemous Act respectively.

Note: Don't use Terminus. Terminus is terrible for Servitude decks.

Blood Scriveneer would help with this deck quite a bit, considering it gives you twice as many options per turn than your opponent once Sire of Insanity hits the field.

You have 6 Izzet Charms.

I personally don't like the ciphers on decks that don't have an unblockable creature, simply because you spend a lot of mana on the spell that should cost a lot less, but because it is repeatable costs a lot more, when it can get chump blocked. If you trade the Undercity Plagues and 2 Swamps for Tormented Souls, then the Midnight Recovery would be a lot stronger since it would draw out a removal spell, but until then allows you to cycle your Relentless Rats to make more Pack Rats.

Also, Immortal Servitude would behoove this deck greatly.

Birthing Pod is expensive, but fills the sac engine quite well.

Add in the Legendary Land that turns all lands into Swamps to enhance Crypt Ghast (I can't remember the name).

Debt to the Deathless x4.

You have 14 mana, you can one shot.

Unless I'm missing something, you won't be able to play half your deck since there is no black mana.

Due to the amount of tokens you can create with this deck, I'd recommend sideboarding Beckon Apparition and adding a playset of Altar's Leap. For Extort, you need spells to play, and draw 2 for 2 + saccing a creature is pretty good, plus you can Extort the Altar's Leap.

In that same mindset, I'd also recommend the Duel Deck Sorin. Produce a token each turn? Yes please.

This is more of a rulings question and it's unlikely that this will ever happen, but for clarity, I'll ask anyway.

What happens if you play a card, then cannot find another match? For instance, in this deck, you Legion Loyalist into Worldspine Wurm, then you get Legion Loyalist again and play it. Would you just reveal your deck and declare can't be found?

Swap out Akoum Refuge for Blood Crypt or Dragonskull Summit and Diabolic Tutor for Increasing Ambition, BAM, STANDARD LEGAL.

Perhaps an Immortal Servitude then. Everything is 4 CMC, so that would fit in nicely.