For the first one: There's something slightly out of place near the Old Hideout.
And the last: If you've bought something from the third tab of the Shop and used it on an Undead, you might have seen the warning that each Undead can only have one of those given to it. But there's a certain Undead you already have that doesn't have that limitation and can take multiple... which can lead to encountering the last Undead.