Heron of Hope copy created with Dollhouse of Horrors does not increase lifegain
Have a Heron of Hope in your graveyard. Have a Dollhouse of Horrors in play.
Activate Dollhouse of Horrors, exiling Heron of Hope and creating a copy of it.
Gain life by any means.
You will gain one less life than you should. The ability of Heron of Hope copy "If you would gain life, you gain that much life plus 1 instead." does not do anything.