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The goal is to understand the low-flux state and long-term behaviour of blazars at high-energies by studying Mrk 421 with a combination of observations from X-rays to TeV gamma rays comma with two INTEGRAL observations of 370 ks each comma one in each of the visibility periods in MayaquestionMarkquestionMarkJune and NovaquestionMarkquestionMarkDec. These observations will be enhanced with snapshots with XMM-Newton and Swift comma and public monitoring programs by Fermi and Swift-XRT. The energy ranges covered by INTEGRAL and FACT are crucial for modelling the SED of blazars we want to investigate the behaviour on timescales of months comma to constrain blazar emission models. Comparing two observations comma we want to investigate if Mrk 421 exhibits a peak shift and thus a tendency to extreme behaviour openParas Mrk 501 and 1ES 2344+51.4closePar.