Blazars are highly variable sources which show variability down to minute time scales. The current generation of Imaging Atmospheric Cherenkov Telescopes like MAGIC are able to probe the spectra of the brightest blazars on short timescales, especially in their flaring states. In this work, we characterize the variability and daily Spectral Energy Distribution (SED) evolution of the archetypal TeV blazar Markarian 421 (Mrk 421) using simultaneous MAGIC Very High Energy (VHE) band (>100 GeV) and Multi-Wavelength (MWL) observations from radio all the way up to gamma ray bands during the November 2009 to June 2010 campaign.

Mrk 421 displayed its strongest flare ever observed in February 2010 when VERITAS measured VHE flux of 15 Crab units above 200 GeV. The source was already in a elevated flux state in January 2010 prior to this extreme flare. We model the SED evolution during January 2010 with a physically motivated single zone leptonic population and study the phenomenology and spectral evolution in the context of a stochastic acceleration scheme. VLBA data unveils contemporaneous ejections of radio features for the first time for Mrk 421. The variability and MWL cross-correlations were analyzed along with the temporal evolution of the daily SEDs to gain insights into the emission processes of this flare that exhibits unprecedented characteristics for the source.