Some people get lucky, some are born lucky and some gain luck through an opportunity that came from nowhere. Clan Feesik is of the last option... somewhat. Back when Clan Pestilens first rose in power, it initiated a purge of several clans, with some conquest and religious conversion thrown into the mix for good measure. Feesik found itself being converted (sort of) when Pestilens saw the squalor these guys were in and thought to themselves "These guys are devoted!". Now, that's nowhere near the truth, but Feesik didn't feel like fessing up (or dying, for that matter) and, since then, they have been "loyal" followers ever since. The only reason that they still live today is the rabid Plague Monks in service to Pestilens, who protect the filthy freaks from their multiple enemies.
To say that Feesik is now one of the biggest butt-kissers in all of Skavendom is an understatement; in fact, it wouldn't be inappropriate to claim that they are the personal "bitch clan", as it were, for Pestilens. Of course, they walk a very treacherous road, as they are often sent to prove their devotion... and run at the first sign of trouble, forcing them to invent lies so ludicrous and magnificent that even a master liar would be impressed!
Though it is doubtful that they deserved this honor, as of Age of Sigmar, Clan Feesik is now a Second Echelon of the Clans Pestilens, even acquiring several thrall clans, like Retchid and Vomikrit. Thankfully, they aren't much more important than that... which is something even their lies can't cover up!