personally i think adding 1 poison counter for 4 mana is pretty insignificant and a bit slow, good if i'm being stalled out but i have enough removal and growth cards that winning is pretty easy to achieve without proliferate
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At first glance i'd say that it would be beneficial to add 4 gemhide slivers, and then try to narrow down some key slivers that you want in your deck, and try to take out some of the less important ones. For example i don't think you'd be using screeching slivers effect much, but but crypt slivers would come in handy a lot more. And giving all your slivers shadow means that you can't block with them so i'd take that one out too. Once you've narrowed them down there's a sliver that lets you cycle and search for a sliver, which can be pretty useful. Lastly i like the idea of using control spells and destroy spells, the thing with this deck is you could use any freaking spells cause it's every colour. My opinion is that in a sliver deck, running a bit more green and then the gemhide slivers makes it faster cause green has cards like rampant growth which i think you should consider adding, since rampant growth and gemhide let you be really prepared for whatever slivers you get stuck with
pretty expensive for 4 cards +land
Yessss first strike and dtouch
4 Gnaw to the Bone 4 Mulch 4 artful dodge add land take out tracker's instincts take out screeching skaab take out evolving wilds take out ghool tree take out lanowar Elves take out birds of paradise Basking Rootwalla Drifter il-Dal Drowned Rusalka Elfish Pioneer Hapless Researcher Hedron Crab Sage of Epityr Sandbar Merfo Screeching Sliver Scute Mob Skyshroud Ranger