Mason Eckhart was once one of Adams best friends.  But somehow things changed.  As Adam became the leader of Mutant X, Mason became the leader of the GSA.  He administrated his building, called Genomex.  He one of the greatest enemies Mutant X ever faced.  After Gabriel Ashlocke came, Eckhart was defeated.  But toward the end of season two, Adam and Mutant X discovered that Mason was back.  On the season finale, he returned as the arch nemesis.  But after Emma's death, it lead to his undoing.  Brennan shot electricity at him and he fell of the balcony, laying on the ground...dead.

Emma met Caleb at a dance club.  He seemed like any modern day type of guy.  But as he kissed her, she said it felt like she was sufficating.  Caleb was a vampire--targeting women to live.  Mutant X tried to arrive to stop him from killing Emma, but they were to late.  But as they killed Caleb, all of the womens souls came back--including Emma.  All of their lives were restored.  But without the life energy, Caleb turned to dust.

Michelle was Emmas best friend from high school.  But when Emma discovered that she was working for the GSA, things changed.  Michelle set Emma up.  But as Emma showed her exactly how bad Genomex was.  Michelle pretended to be good, but actually she only did it to access sanctuary.  Her cyber powers enabled her to gain all of Sanctuarys codes and secrets.  She said she could no longer feel.  But Emma used her powers and made her feel again.  The two were reunited as friends.

Gabrial was a VERY powerful mutant.  He took down Eckhart, and started going after Mutant X.  Emma tried to take control over his soul..but she just wound up getting hurt.  Finally they found a way to destroy this 2,000 year old mutant.

That pic above is not of Billy...iot is of his brother...sorry.  ANYwayyy....Billy is a flame starter.  He has powers that can summon fire.  He even killed his brother whos spirit went into Emma.  Emma (who is really his brother) confronted him and put an end to it all.

In season one episode "Double Vision", Emma's personality was split in half.  The nice, sensitive side and the dark, bad girl side.  The Dark side, was beyond bad.  She even tried to kill Eckhart.  When Mutant X wouldn't help her, then she decided to seek the help of one of Eckharts victims.  Mutant X stopped her, and restored both sides back into the one Emma that we love so much!