Context : The high frequency peaked BL Lac PKS 2155-304 with a redshift of z =0.116 was discovered in 1997 in the very high energy ( VHE , E > 100 GeV ) \gamma -ray range by the University of Durham Mark VI \gamma -ray Cherenkov telescope in Australia with a flux corresponding to 20 % of the Crab Nebula flux .
It was later observed and detected with high significance by the Southern Cherenkov observatory H.E.S.S .
establishing this source as the best studied Southern TeV blazar .
Detection from the Northern hemisphere is difficult due to challenging observation conditions under large zenith angles .
In July 2006 , the H.E.S.S .
collaboration reported an extraordinary outburst of VHE \gamma -emission .
During the outburst , the VHE \gamma -ray emission was found to be variable on the time scales of minutes and with a mean flux of \sim 7 times the flux observed from the Crab Nebula .
Follow-up observations with the MAGIC-I standalone Cherenkov telescope were triggered by this extraordinary outburst and PKS 2155-304 was observed between 28 July to 2 August 2006 for 15 hours at large zenith angles .

Aims : We studied the behavior of the source after its extraordinary flare .
Furthermore , we developed an analysis method in order to analyze these data taken under large zenith angles .

Methods : Here we present an enhanced analysis method for data taken at high zenith angles .
We developed improved methods for event selection that led to a better background suppression .

Results : The quality of the results presented here is superior to the results presented previously for this data set : detection of the source on a higher significance level and a lower analysis threshold .
The averaged energy spectrum we derived has a spectral index of ( -3.5 \pm 0.2 ) above 400 GeV , which is in good agreement with the spectral shape measured by H.E.S.S .
during the major flare on MJD 53944 .
Furthermore , we present the spectral energy distribution modeling of PKS 2155-304 .
With our observations we increased the duty cycle of the source extending the light curve derived by H.E.S.S .
after the outburst .
Finally , we find night-by-night variability with a maximal amplitude of a factor three to four and an intranight variability in one of the nights ( MJD 53945 ) with a similar amplitude .

Conclusions :