Mutagen is, as the name implies, a mutagenic substance capable of producing permanent physical effects on anything organic that is exposed to it. In the video games based on the 2007 CGI film, it is, in particular, the genesis of the Ninja Turtles and Splinter's mutations.
In the 2007 TMNT Game Boy Advance game, the mutagen "capsule" is one of the items placed on Splinter's trophy shelves, acquired by beating a stage without losing a life.
Trophy description[]
The vessel of toxin that birthed this family's strange fate.