Flanking

Flanking is the tactic where you go around the enemy, them surprise and kill them. It is best done with something distracting them, such as a teammate engaging in a fight. This can only be done if there is an alternative tunnel going to the enemies' position and is not ideal if that tunnel is very far away.

Performing
To flank, first your team and the enemy must be at a stalemate, next, you must find a tunnel or secret tunnel leading to the enemies position and go through it. Once you reach it, you must then kill the enemy swiftly, just like in an ambush. This tactic is rare and not very efficient but can turn the tide in a battle.

Gallery
Video added here later.

Trivia

 * This tactic is fan made and has no official name.