Counter heavy proactive control with a distruption-based aggro deck in the Legacy format
So, we know you are looking more for a heuristic for how to play your deck as is (or with minimal changes) against an attrition based opponent playing a pox/gate like deck. 

The aim of your opponent's deck is to slow the game down as much as possible, so it can abuse its central cards to gain an incremental advantage (usually though the difference in how the values of your respective resources at the time Pox is cast are rounded). To beat this kind of strategy, you either need to come in underneath it, by killing it before it can accrue enough advantage, or go over the top of it, by negating the advantage it is trying to accrue (investing in resources it cant/doesnt interact with, such as artifacts/enchantments) or preventing it from gaining that advantage at all, such as with countermagic.

The most obvious answer (for your deck) is to mulligan aggressively to aggressive hands with lots of efficient, aggressive creatures, and try to overwhelm them before they can lock you out. Creatures that you can discard to the battlefield (some of which you have mentioned) augment this strategy.

Pox decks tend to rely heavily on buying back from their graveyards,finding a way to limit that (such as Deathrite Shaman or Scavenging ooze removing Bloodghast) should help make that strategy harder. On the subject, scavenging ooze provides a good way to rebuild following a wrath effect.

Similarly, as they attack against the axis of lands and creatures, combating that by playing artifacts, enchantments, and planeswalkers that make their strategy problematic is useful. Elspeth, Knight Errant is a very good planeswalker to consider for your deck, and the various swords (particularly Sword of feast and famine) will work well with her tokens to let you stay in the game with resources your opponent can't easily control.

If land destruction is going to be an issue, fetchlands for basics for the first few turns may well be the best way to mitigate that. Pox/Smallpox wont be affected, but at least wasteland will have less impact.

Silence in your opponent's upkeep or drawstep could give you a valuable Time Walk against them, allowing you to further establish yourself. Lingering souls will give you enough to work with to protect your bigger creatures from a few edict effects, particularly if you have black mana to flash it back.

There isn't any way, as a deck built around a board presence of a small number of highly effective creatures, for you to overcome a deck like this in terms of attrition. As is, your only option is to be aggressive and cross your fingers. This IS a strategy, and one that you can try to maximize. You know which of your cards are the most aggressive, and you can mulligan to try and get a hand that will kill your opponent quickly. A Mother of Runes, Knight of the Reliquary reliant hand will probably struggle, but other hands with more aggressive creatures would do better.

With the possibility of making some changes, the above options should be plenty of food for thought, it is worth bearing in mind though that every advantage gained here is potentially (I would say almost certainly) a loss in another match-up. The minimal impact would probably be some Silences, or to consider Lingering souls and/or an Elspeth, Knight Errant or 2, with Swords to back up your tokens. I can't tell you the best combination, but these are all the options I can think of for ways to combat this strategy. It's not for a tournament, so you have plenty of room for experimentation and finding what works best for you.