How do you get the Team Builder - Assassin?
It was a mission or event reward. Riot's description in the client reads: “Earned by playing 5 games as an Assassin champion in Team Builder during the 2014 Teambuilder event.”
Is the Team Builder - Assassin still available?
No. Riot tied the Team Builder - Assassin to 2014 (mission reward), and it does not normally bring back past event rewards or bundles.
