Antimatter is basically the opposite of matter. Matter is composed of electrons, protons and neutrons. Meanwhile, Antimatter is composed of positrons, antiprotons and antineutrons. Antimatter used to be a theoretical substance, which when combined with a matter results in gamma radiation. The applications of this substance are nearly endless as it has a high energy potential.
With the substance having moved from theoretical to being produced and observed, the negative ramifications have sprung to life. To date, the cost of producing antimatter has been in the range of hundreds of millions for a few atoms. To produce a gram of antihydrogen it would cost in the billions.
The cost of production is not the only downside however. The material can only exist in a perfect vacuum, or at the very least in the absence of actual matter. The implication is that, before 2011, antimatter had only been produced for 0.2 seconds. As of 2011 however, antimatter was able to be sustained for up to 1000 seconds. The only difference between the two is the fine-tuning of the capturing methods.
Applications of antimatter include high energy military weapons, medical research and space exploration. Until antimatter capturing and production has been refined though, antimatter death ray guns will remain a thing of fantasy.