Spiders have few viable legendary commanders aside from Ishkanah, Grafwidow and Thantis, the Warweaver, so there's plenty of room for casual Commander players to build a new Spider deck around Shelob to take advantage of its intriguing abilities
Modern isnt that fast right now, but there could be a future where your deck plans on comboing off after leading a turn on a cantrip where Serum Visions being slower matters
(5/3/2019) If a permanent has in its mana cost, X is considered to be 0
Its fairly easy to commit crimes in decks built to do that, and getting 3/3 Zombie Rogue tokens as a result is strong
The deck starts by casting efficiently-costed creatures with strong secondary abilities including Thornvault Forrager (ramp, squirrel fetch), Osteomancer Adept (deathtouch, reanimate), Valley Rotcaller (menace, drain), Vinereap Mentor (food tokens), Bonecache Overseer (draw)