The Negative Zone
The Negative Zone is an alien universe with several characteristics that distinguish it from our own. First, and most importantly, it is composed entirely of anti-matter. Anyone or anything that moves from one universe to the other must reverse its polarity on a molecular level or be instantly annihilated. Second, it is a mature universe that has already started to contract (ours is still expanding); eventually, it will implode. Third, time passes at a faster rate relative to ours. Fourth, a still unknown factor (possibly lack of water) makes evolution difficult, because much of the Negative Zone is still uninhabited. The best-known beings from the Zone include Annihilus and Blastaar.