  We present optical photometry and spectroscopy of SN2005ip for the first 3yr
after discovery, showing an underlying Type II-L SN interacting with a steady
wind to yield an unusual Type IIn spectrum. For the first 160d, it had a fast
linear decline from a modest peak absolute magnitude of about -17.4
(unfiltered), followed by a plateau at roughly -14.8 for more than 2yr.
Initially having a normal broad-lined spectrum superposed with sparse narrow
lines from the photoionized CSM, it quickly developed signs of strong CSM
interaction with a spectrum similar to that of SN1988Z. As the underlying
SNII-L faded, SN2005ip exhibited a rich high-ionization spectrum with a dense
forest of narrow coronal lines, unprecedented among SNe but reminiscent of some
active galactic nuclei. The line-profile evolution of SN 2005ip confirms that
dust formation caused its recently reported infrared excess, but these lines
reveal that it is the first SN to show clear evidence for dust in both the fast
SN ejecta and the slower post-shock gas. SN2005ip's complex spectrum confirms
the origin of the strange blue continuum in SN2006jc, which also had post-shock
dust formation. We suggest that SN2005ip's late-time plateau and coronal
spectrum result from rejuvenated CSM interaction between a sustained fast shock
and a clumpy stellar wind, where X-rays escape through the optically thin
interclump regions to heat the pre-shock CSM to coronal temperatures.
