Skaven armies are famous for two things; the collosal numbers they slap on the table and the ramshackle war machines they drag behind them. The Plagueclaw is one such machine. You may be more familiar with this weapon of war from seeing it shoehorned into a Maggotkin list, or spamming them to win Mortal Empires in Total War Warhammer (I have no regrets, Mazdamundi had it coming). It isn't often fielded in any chaos list not of Pestilens or Nurgle, a distinction that seperates it from the Warp Lightning Cannon and Stormfiends.
Shooting for the Moon
This catapult outranges 90% of the units in Age of Sigmar, and doesn't even need to see those units to hit them. Furthermore, as appropriate for something that lore-wise just carpet bombs the enemy with sludge, it gets significant benefits for targeting units that have more than 10 models (Not 10 or more, MORE than 10). It's rend is -2, shockingly brutal for a ranged weapon, which compensates for not recieving the anti-horde bonus if targeting elite units with good armor saves like Stormcast Paladin units or Kurnoth Hunters.
Landing in the Dumps
Thank god this thing got a point reduction going into AOS2, or I wouldn't even be bothering to write this in the first place. Despite the above benefits, the thing just cost far too much to have more than 1 of as a token threat to hordes during AOS1. 160pts is much more bearable for it's often unreliable nature, and while it's unreliabilty can be directly combatted with the Foulrain Procession batallion, it's also a 700pt sink that will prevent you fielding a decently sized force, something critical to victory with Clan Pestilens.
I personally plan to be upping my catapult count to 2 heading into AOS2, the point reduction was nice and makes it easier to justify this unit as a support choice.