Primeval fire is too good for control builds. You should probaly make it cost 3 or four. Compare it to Phyrexian Totem, which is played in some control decks as a hard to deal with finisher.
I assume that for Darkness Summoner the tokens come into play under your control?
Shadow world, in my humble opinion, needs to be more exiting.
First of all, i love tainted. It has so much design space and is quite original. Now, back to the Sea of Oblivion problem. I think that it depends on how good you want it to be. If you want it to be format defining, this version would work well -
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Sea of Oblivion
Land
Lands cannot be tapped for mana.
Remove to top two cards of your library from the game: Add U or B to your mana pool. Any player may play this ability
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However, a weaker one would be like this -
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Sea of Oblivion
Land
Put the top card of your library in your graveyard, T: Add one mana of any color to your mana pool. Any player may play this ability.
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I assume that for Darkness Summoner the tokens come into play under your control?
Shadow world, in my humble opinion, needs to be more exiting.
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Sea of Oblivion
Land
Lands cannot be tapped for mana.
Remove to top two cards of your library from the game: Add U or B to your mana pool. Any player may play this ability
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However, a weaker one would be like this -
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Sea of Oblivion
Land
Put the top card of your library in your graveyard, T: Add one mana of any color to your mana pool. Any player may play this ability.
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