Badass Creed/Western Animation

"One shall stand, one shall fall." Optimus Prime versus Megatron. More than just a one-liner, it has been cropping up in the new movies as well as video games.
- It was used first in the original Transformers movie (in the 1980s), at the beginning of the final battle between Megatron and Optimus Prime, and the one who died was Prime. To anyone for whom this was a pivotal moment in Transformers, and perhaps storytelling in general, the phrase retains the capacity to terrify the hell out of you. Its use in the 2007 Transformers movie was especially effective for creating actual tension.
- To be fair, Prime won the fight, and Megatron only "survived" because Unicron remade him as Galvatron.
- This can be considered a Mutual Kill.
Darkwing Duck has two. One is his introduction speech, with variations on "I am the terror that flaps in the night...I am Darkwing Duck.", and the other is far more badass "Let's Get Dangerous"
sengoku musou gives us a little badass gem by ranmaru mori: "My body is a sword, and this place i stand in is a burial ground. Let those who wish to die step forth!"
Arguably, the opening sequence lyrics of W.I.T.C.H.
"I am Vengeance. I am the Night. I. AM. BATMAN!"
- The Justice Guild "Let Justice Prevail."
Just five little words: "We. Are. Kids! Next! Door!"