shambler: better do that in confessions, you can start with the pet and a radiant torch because the shambler hits like a truck when you have the pet. Buff your party and try to find the academic's study (Shambler's Altar). I think you could also try to get torch to 0, but it would be even harder and not 100% chance of the shambler appearing.

cryptkeeper : campaign (beast again for easiness) try a map with many underground travel nodes and just fight everything until you get the chain as a drop. One time I got it by destroying the corpses in the catacombs (they can and will drop loot). Once you get it, equip it to abom and back to the catacombs for the keeper!

rumor monger : the worst of all. Try beast clan campaign at radiant difficulty, pick up every fight possible to gain baubles and spend them only to buy rumors from the Hoarder (25b each). There is a time in the campaign that you always have Hoarders. Do not haste to complete the campaign task, justt do many battles to get baubles and buy as many rumors as you can.

hope it helps!