If you're counting on Winged Sliver or Muscle Sliver or any other boost to carry you through combat, then a removal spell on the key ability can destroy your entire team, and even with Hibernation Sliver available such a blow is often crippling
3 full-art Supporter cards
Brushfire Elemental Creeping Trailblazer Grove Rumbler Jegantha, the Wellspring Leafkin Avenger Living Twister Morselhoarder Omnath, Locus of Rage Pako, Arcane Retriever Phylath, World Sculptor Rubblehulk Rumbling Slum Vibrance Wilderness Elemental Wildsear, Scouring Maw Zendikar Incarnate
She could potentially be free, though realistically were looking at 4 drop if we play her when first able excluding ramp we might get
Dryad of the Ilysian Grove Brad Nelson questioned the brokeness of Dryad of the Ilysian Grove last week, but it seems obvious to me
Win conditions specified on individual cards