Confused by the use of was in the relative clause of the following sentence:
Zerfrisst die Rüstung des Ziels, was dessen Rüstungswert deutlich beeinträchtigt.
Erodes the armor of the target, significantly reducing its armor-value
or in an awkward, but more literal translation:
Erodes the armor of the target, whose armor-value becomes reduced.
I am assuming that the dessen here is a genitive-case article that corresponds to the modified noun Ziels. My question is: is the was here necessary? if so, why and how does it affect the meaning?