Yorick's Pets still have resistances they aren't intended to
https://www.youtube.com/watch?v=RUVveKdiU_U&feature=youtu.be http://leagueoflegends.wikia.com/wiki/Yorick#Mist_Walker http://leagueoflegends.wikia.com/wiki/Yorick#Maiden_of_the_Mist http://gameinfo.na.leagueoflegends.com/en/game-info/champions/yorick/#spell-passive
There is leftover code from Yorick's old state, causing all of his pets to incorrectly halve all AoE damage dealt to them, even damage that is supposed to be %HP.
As you can clearly see, there is nothing in the spotlight, wiki, game page, or client that says they do this. It is not intended. His old pets did not have a base HP and were not so numerous, so they had AoE reduction. The new ones should not but are bugged to do so, EVEN the Maiden, who has up to 4000 HP.