When THG/Hag of Scoured Thoughts' ability is activated, any triggered abilities of cards moving from library to graveyard or otherwise triggered when milled do not properly go on top of the stack.
This causes HoST ability to always finalize before activated abilities are supposed to trigger on the stack.

Putting it lightly, stuff like this is why I'm not a fan of Alchemy. It should be like DoTP. Legal within its own sets, but not a part of historic.
Or... DoTP should retroactively be added to historic. Please give us more cancer so we can balance out the cancer. ( ఠ ͟ʖ ఠ)