1) Fog Patch . I'm not sure how a patch of fog can work so differently than regular Fog . Apparently, Fog wil stop all damage from being dealt, but just patches of Fog will just prevent creatures without trample from dealing damage to players (if they are also blocked by creatures, damage will be shared).
I've always thought that Fog works by making it impossible to safely navigate. Even if you're defending your home turf, you can't remember where each stone and hole stands. What's more, a stumbling warrior could blindside you. I think that Fog makes it very hard (but not impossible) to continue the battle, so it is called off by the planeswalker.
A fog patch spell assumes that it is an aimed phenomena. The caster aims the fog into certain patches that 'stick' to the creatures. They are surrounded by a fog patch that follows them around. A battlefield with several units on it would look like several clouds wandering like stars in the sky. The difference here is that the creatures can still deal damage if they stumble into each other.
One could imagine that a trampling wurm could do a lot of 'stumbling' and be able to hit something worthwhile despite being surrounded with fog. Likewise, you could place a 3/3 to intercept an attacking a 1/1. Planeswalkers can sense who is where, but the creatures themselves cannot attack properly with their sight blurred.
I might allow creatures that are affected by Fog and similar cards to make a stunt check to naviagte the bad weather. The DC would be high, with penalties ranging from -1/-1 counters to death (or even exiling, assuming that they wander into a Faerie realm).
2) Mana Cache . Without mana burn, this card is worthless, and that's being generous. Heck, with mana burn, it was a wacky rare. Now, it's only worthwhile if you're playing against Draw-Go. The average player will simply tap any excess lands to prevent you from getting free mana.
I could make the Cache try and compel your opponents to leave lands untapped, but I'd rather just make it an effective hoser for Draw-Go. I think that upping the mana accessible from the Cache larger. Maybe make it 3 mana. Perhaps the Cache amplifies mana stored inside it. Its chaotic growth is what makes it so easy to have it stolen from you. Mana Flare doubles your mana for the same price; Mana Cache should be better for being niche. I don't want to make it too much larger: Scars of Mirrodin has a lot of charge counter helpers, especially Proliferate.
3) Reverent Silence . This set's theme of giving life away instead of paying for the mana was an interesting concept. In decks, I've only ever seen it used as a tool with False Cure . Flavourfully, the deep silence allows the planeswalker to gain some cosmic insight and clear the battlefield of enchantments and other artificial magics.
Describing the life given as flavour is a little tricky. I think it is still some kind of impartment of wisdom given to every opponent. I don't think it could be a Resource: if temples are built around whatever cosmic truth imparted to you, this life is not those temples. I think the life should be added to a pre-existing NPC or Planeswalker, as wisdom granted to your enemies that they might share your enlightenment. It could be divided amongst up to 6 NPCs and/or planeswalkers. The wisdom makes them hardier. D&D Monks and Paladins grow stronger from the faith, and whatever wisdom you impart to them makes them stronger.
4) Stronghold Gambit . I get the balance reasoning for why the smallest creature is the one that enters the battlefield. It reduces the brokenness of the card. It creates some interesting tensions when Emrakul, the Aeons Torn comes into play with Autochthon Wurm . It combos well with discard.
Flavourwise, I'm not sure how the gambit works. The art doesn't help out, as both groups of creatures in the art are on the same side, and wouldn't be directly competing with each other. Using my imagination, I guess that raiders on the Stronghold use their bigger creatures to create a diversion for the smaller forces to enter play. The guards focus on the Wurm, and allow the Warriors in.
So how can your opponent, whom you're running the gambit against, benefit from this? Perhaps, like in any gambit, it can go completly sidewises. Your foe can gain knowledge of it and use it as a trap. If your goblin warriors are attempting to tunnel inside the Stronghold, you can intercept their handlers and force them to aid your kobolds.