These permanents sit on the board and try to choke your mana or stop
your engine loops from working by making them too expensive to
execute.
Aura of Silence:
It taxes your enchantments by three mana, which makes hardcasting painfully
slow. On top of that, it can sacrifice itself to destroy whatever key
enchantment you finally do resolve. This is exactly why the sideboard
splits between Seal of Cleansing and Disenchant—Disenchant is a clean two-mana instant that Aura's tax doesn't
touch.
Gloom:
It taxes every white spell and white activated ability by three mana,
which can badly slow down Replenish, Swords to Plowshares, Opalescence, and Parallax Wave. The good news is Gloom only touches white. Your whole blue
card-selection package (Attunement, Frantic Search, Intuition) and your counters (Mana Leak) work just fine. The bad news is that it also affects the
activated abilities of white enchantments. Against heavily black
decks, save your early counters for Gloom itself. If it does
resolve, use your Ancient Tomb ramp to pay through the three-mana tax over a long game; Disenchant and Alter Reality are good solutions too. The issue with the Seal of Cleansing here is that it takes too much time to destroy a Gloom, usually 5 mana
to cast, and 3 to activate; Disenchant reduces that to only 5.
Winter Orb:
Replenish is built around three- and four-mana spells, so only untapping
one land a turn really slows down your setup. Get rid of it right away
with Seal of Cleansing or Disenchant. If it sticks, Ancient Tomb is great because you get two mana off the one land you untap.
Dystopia:
Every one of your upkeeps, you have to sacrifice a green or white permanent.
Left alone, it chews through your Opalescence, Parallax Wave. The key points: Dystopia costs the opponent more and more life
each upkeep, and it only hits green and white—so your Attunement is completely safe. Just build your combo up in the graveyard without
laying out white permanents early, and when you're ready, cast Replenish onto a full board. At that point, sacrificing one spare white permanent
to the upkeep trigger doesn't matter, and you swing for the win. Keep
in mind that if you assemble the Opal Wave combo, Dystopia is a creature,
and you can remove it with the wave.