Do you need the DLC to get the Full Flock" achievement?

[Doc]

I'm trying to get all of the cultist skins but I can't buy them from the shop and I they don't drop from god tears anymore. Do I need to get the DLC to get the rest or is there a way to get them and the achievement without buying it?

[Cairn.L]

Nope.
There is not a single achievement in the game that requires purchasing any of the DLCs.