Ruby Storm's main-deck win condition is Seize the Storm, a sorcery, so Envelop is a precise answer that can simply counter it outright (it also hits their sorcery-speed card flow like Glimpse the Impossible, Reckless Impulse and Wrenn's Resolve). Arms of Hadar is a useful sweeper here because their cost-reducer creatures (Goblin Anarchomancer, a 2/2, and Thornscape Familiar, a 2/1) both die to -2/-2, which slows their mana-cost reduction and the chain of spells they rely on; it can also serve as a backup against a resolved Seize the Storm token by shrinking it by 2/2 for the turn before it attacks. Cut slower, grindier cards like Baleful Strix and Utrom Monitor that don't close games fast enough against a deck trying to combo off in one explosive turn.