Amazing combo - Rakdos the Defiler + Prince of Thralls. If Rakdos deals combat damage, you get half of your opponents non-demon permanents or they must lose 3 life for each card you don't get. The only cost is half of your non-demon permanents, but you will have very few of them.
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So? One of the combos allows you to make your islandwalkers unblockable by using an Island and Quest for Ula's temple to pull Sky Swallower and give your opponent an Island. The only cards that need to be pulled by Quest for Ula's temple to work are Nemesis of Reason and Simic Sky Swallower. Alternative strategies include using Quicksilver fountain to turn their lands into Islands, or Stormtide Leviathan to make them function as Islands. Stormtide Leviathan also functions quite nicely because it can turn the other lands into islands so that you can sacrifice them when you don't need them anymore for the effect of Leviathan.