The point of Pox is to hurt everyone equitably, not equally, and to turn that to your advantage by having less to lose. I don't care about Mindslicer if you're running hellbent triggers or functional hellbents like Mindstorm Crown and Blood Scrivener. If you're dropping Death Cloud you don't care about your sac fodder creatures like Bitterblossom tokens, and you run extra heavy on artifact ramp to live without land. What do you care about Lethal Vapors when your commander is Skithiryx, the Blight Dragon and can be regenerated?
Use more, less valuable permanents to trade with your opponents more valuable, less numerous permanents while attacking their hand to limit how much they can protect and produce. Many decks are built around high value threats that are still only individual cards, like Birthing Pod for example, and don't have the fodder to keep up with a deck built towards attrition.
"All player" effects are more bang for your buck in terms of mana than any "opponents" or "target player" effects, and you control when you play them so that they give you the greatest advantage.
May 13, 2018 4:13 p.m.
It's a war of attrition. Smallpox is in your favor if you don't have a creature to sac, or if you discard something like a Bloodghast in the bin. Slowing your opponents down by depriving them of several resources with a single spell is a great way to gain quick and lasting advantage.