Basic Trope: A previously unseen character makes himself known with a dramatic attack.
Straight: Emperor Evulz has overwhelmed Bob, who laid battered on the ground. Evulz raised his sword to deal the final strike, when suddenly Alice crashed from the window and delivered a kick to Evulz' face with much gusto.
Invoked: Alice waited until the final moment because attacking then would be the least predictable outcome for Evulz.
Exploited: EVERY. SINGLE. ATTACK.
Defied: Alice had a sniper rifle next to her and could see Evulz through the window.
Discussed: "Man, Alice really likes breaking through things to deliver a kick."
Conversed: "She came out of nowhere! Why didn't she attack before?"
Implied: Alice is shown breaking into a building. A second later, it zooms into the building and a mook is shown knocked out next to her.
Deconstructed: Evulz has predicted an unexpected attack and closed the battle with Bob inside a barrier.
Reconstructed: Alice has secretly developed a technique that can break through the barrier. She strikes Evulz while the latter thinks they are now safe from ambushes.
Plotted A Good Waste: A villain is bigged up to set the tone for the arc, and is defeated in a single kick from behind by Alice, creating a humorous anticlimax.
Played For Drama: A hero's celebration is brutally ended after a villain strikes from nowhere and kills one of them, leaving the remainder in shock for a few moments while the villain presses the attack.