Twitch's design closely resembles that of the Skaven, a devious and warlike race of anthropomorphic rats from the Warhammer Fantasy franchise. The Medieval skin reflects this similarity more than his original skin.
Spray and Pray is a generic phrase used to describe the random spraying of bullets with an automatic weapon hoping to hit something.
Deadly Venom displays an "X" symbol upon reaching 6 stacks.
Twitch's title is likely a reference to the Bubonic Plague, which killed millions in Europe during Medieval times, and was transmitted by rats or more specificly, their fleas.
Skins
Gangster Twitch may be a reference to the Toon Patrol weasels from Who Framed Roger Rabbit, or to the actor James Cagney who is famous for portraying a gangster and his misquoted line, "MMMmmm, you dirty rat!".
It is also believed to be a reference to Pinstripe Potoroo, the fourth Boss in the first Crash Bandicoot.
Medieval Twitch was conceived by the 2 people that first hit 350 friend referrals: Grez and Greyrir Wolfwood. Grez picked the champion that would receive the skin, and Greyrir Wolfwood designed a "Medieval Twitch, with a fleur-de-lis on his cape, and a pot on his head". The idea was given to the Riot artists and Medieval Twitch was released a few months later.
Medieval Twitch holds the distinction for being the rarest skin in the game.