One person I was really impressed with was Scrufizzer.in 2011. He released loads of music which was big in the Grime scene and featured with Lethal Bizzle, Lady Leshurr, Marger, No Lay and many more. Although we haven't seen a mixtape from him yet, I really think he will release one this year. For a good start to 2012 he has kindly done a freestyle which he smashed in my opinion.
