Here is the fastest way to get this achievement.
First, you should probably start by doing all the other ranked MP achievements, since these matches will count towards your 100 matches played.
Then, use the following method in player matches with a boosting partner.
1) Create a private player match. Put the Battle Count to 1, make it private: room size=2 & private slot=1, and invite your friend.
2) One player will be winning by Ring out. If you are the winning player, choose a big character such as Nightmare or Astaroth. Your friend picks a small character such as Xiba or Viola.
3) Pick the map "Shrine of the Snake God Palgaea". It is the second to the left when you are at the selection screen. You'll start on a balcony with a pit right next to your fighters.
4) Start the match and spam
to skip the opening cutscenes.
5) Sidestep to the side of your opponent, then run towards him and press
to trip him, which will make him fall to his death. You'll get a win in 3 to 4 seconds.
during the win animation, then press
to return to lobby.
7) Repeat steps 2-6 99 times :)