Ridiculous Sliver, this is. It's bad enough that the UW ones will be large, flying and uncounterable, now they're all Force Spikes?? Holy shit, UW Sliverfish is the best deck EVAR
Sooo yeah, um, I think it's undercosted. However, by even raising it by one colorless mana you make it ass. Boo, it had to be one of those 'tough' cards

What if it were Tap-Sac, or U-Sac, instead of just sac?