  PKS 2155-304 is a blazar located in the Southern Hemisphere, monitored with
the High Energy Stereoscopic System (H.E.S.S.) at very high energy (VHE, E>100
GeV) $\gamma$ rays every year since 2002. Thanks to the large data set
collected in the VHE range and simultaneous coverage in optical, ultraviolet
(UV), X-ray and high energy $\gamma$-ray ranges, this object is an excellent
laboratory to study spectral and temporal variability in blazars. However,
despite many years of dense monitoring, the nature of the variability observed
in PKS 2155-304 remains puzzling. In this paper, we discuss the complex
spectral and temporal variability observed in PKS 2155-304. The data discussed
include VHE $\gamma$-ray data collected with H.E.S.S. between 2013 and 2016,
complemented with multiwavelength (MWL) observations from Fermi-LAT, Swift-XRT,
Swift-UVOT, SMARTS, and the ATOM telescope. During the period of monitoring,
PKS 2155-304 was transitioning from its lower state to the flaring states, and
exhibiting different flavors of outbursts. For the first time, orphan optical
flare lasting a few months was observed. Correlation studies show an indication
of correlation between the X-ray and VHE $\gamma$-ray fluxes. Interestingly, a
comparison of optical and X-ray or VHE $\gamma$-ray fluxes does not show global
correlation. However, two distinct tracks in the diagram were found, which
correspond to the different flaring activity states of PKS 2155-304.
