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The greatest movie of all time. There's so much body dismembering and excessive amounts of blood that it keeps you entertained throughout the movie.
Guy 1: Man, i saw Ninja Assassin the other day

Guy 2: Oh me too, there's so much blood i could have sworn i was watching a documentary on PMS!

Guy 1: o.O
by The Notorious Poon Slayer April 15, 2010
Happy St. Patties Day!
(v.) to excessively and wildly dismember a person's body using Asian weaponry (gallons of blood are typically lost from the victim's body when being ninja assassined)
Witness 1: Dude you completely ninja assassined that guy!
Assassin: Yeah I'm going cut his limbs off too.
Witness 2: Holy shit! There's blood everywhere!
by Kushikime December 01, 2009
Happy St. Patties Day!
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In roleplaying games (especially ones not centred around physical conflict), a character who has been designed expressly to be extremely powerful in a fight and/or extremely stealthy.
The term is frequently used sarcastically, as creating such a character is often a sign that the person doing so still thinks he's playing D&D.
Did you see the new guy's character? He's a complete ninja assassin.
by Whybird June 08, 2004
Happy St. Patties Day!