Abnormal is a scheme where players have to kill their own worms within as few turns as possible, using weapons present in the Intermediate scheme. The idea, although it might sound simple, actually leads to interesting battles between players trying to get bigger combos than their opponents.
An average Abnormal round lasts from 4 to 6 minutes, so a best of 5 game shouldn't last longer than a Team17 game.
See the Scheme Info link for example replays.
Any open random map without bridges can be used. Good luck and have fun.