Wrote up a big list of slivers. Naturally I'm going to base them somewhat on physical appearance and somewhat on assumptions (for materials and the like). Most of them will likely be made out of muscle/sinew with bone for attacks and such.
I'll post this list here in case anyone else wants to try making some or has any suggestions regarding specific varieties.
all slivers savage, some maybe good/evil
name p/t card rarity cost possible abilities
acidic 2/2 uncommon bla/red syndrome spit attack?
armor 2/2 uncommon whi/2 tough skin/chitin?
barbed 2/2 uncommon red/2 stronger attack mat, extra strong single attack?
basal 2/2 common bla/2 ITEMCORPSE?
battering 4/4 common red/5 area effect attack via dust?
blade 2/2 uncommon red/2 [similar to barbed but older card]
bonesplitter 2/2 common red/3 significantly stronger attack mat?
brood 3/3 rare gre/4 large littersize?
cautery 2/2 uncommon red/whi semi-suicide attack?
clot 1/1 common bla/1 regeneration?
crypt 1/1 common bla/1 super-regeneration?
crystalline 2/2 uncommon whi/blu special mat makeup?
darkheart 2/2 uncommon bla/gre syndrome/ITEMCORPSE?
dementia 3/3 uncommon blu/bla/3 syndrome attack?
dormant 2/2 uncommon blu/gre/2 slow and tough?
essence 3/3 rare whi/3 [don't know yet]
firewake 1/1 uncommon red/gre/1 fast?
frenetic 2/2 uncommon red/blu/1 [don't know yet]
frenzy 1/1 common bla/1 high anger/speed?
fungus 2/2 rare gre/3 leaks syndrome mat?
fury 3/3 uncommon red/5 powerful attacks/high speed?
gemhide 1/1 common gre/1 ITEMCORPSE?
ghostflame 2/2 uncommon bla/red [don't know yet]
harmonic 1/1 uncommon gre/whi/1 [don't know yet]
heart 1/1 common red/1 fast?
hibernation 2/2 uncommon blu/bla [don't know yet]
homing 2/2 common red/2 [don't know yet]
horned 2/2 uncommon gre/2 area attack?
hunter 1/1 common red/1 high anger/activity?
lymph 3/3 common whi/4 tough skin/chitin?
magma 3/3 rare red/3 [don't know yet]
mesmeric 2/2 common blu/3 [don't know yet]
metallic 1/1 common 1 [artifact] [don't know yet]
might 2/2 uncommon gre/4 stronger in general? slow?
mindlash 1/1 common bla [don't know yet]
mindwhip 2/2 uncommon bla/2 [don't know yet]
mistform 1/1 common blu/1 special mat makeup?
mnemonic 2/2 uncommon blu/2 [don't know yet]
muscle 1/1 common gre/1 stronger in general?
necrotic 2/2 uncommon whi/bla/1 semi-suicide attack?
opaline 2/2 uncommon whi/blu/1 [don't know yet]
plague 5/5 rare bla/bla/2 necrotic dust?
plated 1/1 common whi tough skin/chitin?
poultice 2/2 common whi/2 regeneration?
psionic 2/2 rare blu/4 semi-suicide attack?
pulmonic 3/3 rare whi/whi/3 flies, super-regeneration?
quick 1/1 common gre/1 [don't know yet]
quilled 1/1 uncommon whi/1 mat spit attack?
reflex 2/2 common gre/3 fast?
root 2/2 uncommon gre/3 [don't know yet]
screeching 1/1 common blu [don't know yet]
sedge 2/2 rare red/2 [don't know yet]
shadow 1/1 common blu/2 semiphysical material makeup?
shifting 2/2 uncommon blu/3 semiphysical material makeup?
sidewinder 1/1 common whi [don't know yet]
sinew 1/1 common whi/1 stronger in general?
overlord 7/7 mythic [1x]all [don't know yet]
queen 7/7 rare/mythic [1x]all [don't know yet]
silversmith 1/1 uncommon 2 [artifact] [don't know yet]
spectral 2/2 uncommon bla/2 semiphysical material makeup?
spined 2/2 uncommon red/gre [don't know yet]
spinneret 2/2 common gre/1 [don't know yet]
spitting 4/4 common bla/4 ranged syndrome attack?
synapse 3/3 rare blu/4 [don't know yet]
synchronous 4/4 common blu/4 [don't know yet]
talon 1/1 common whi/1 [don't know yet]
telekinetic 2/2 uncommon blu/blu/2 stunning syndrome attack?
toxin 3/3 rare bla/3 deadly syndrome?
two-headed 1/1 common red/1 [don't know yet]
vampiric 3/3 uncommon bla/3 bloodsuck attack?
venser's 3/3 common 5 [artifact] [don't know yet]
victual 2/2 uncommon gre/whi [don't know yet]
virulent 1/1 common gre syndrome attack?
ward 2/2 uncommon whi/4 [don't know yet]
watcher 2/2 common whi/3 agile yet weak?
winged 1/1 common blu/1 flying?
Another idea would be making a civ out of them. If I decide to do that, it'll probably be in addition to having "wild" versions.