First, for make it rain you should have 4/5 or 5/5 of the requirements needed.
Second, Couldbloom is mainly use for make a certain potion (Talk with a tree), as well as Ghost talk.
Third, You have to read Note 17 which gives you hints on where to find the "Painted forest" (If i'm not wrong)
It haves a trick too, but if you bring an axe and are a bit careful, you can get the reward from surviving the trap, and get a hint for where is the real treasure.
Fourth, Is better you read the previous comments a few pages ago. Me and Somebody95 were talking about how to do it. But is better that you first complete and explore what you have to do in the forest, by the moment. When you feel comfy enough, jump into do this "Dimensional jump".
Fifth, There is two chests. One opens with a "Fragile key", and the other opens with a "Rusty key". The "Rusty one", is a whole long puzzle that might take you a few dream, only for get everything set up for just start the process. (And don't care that much about this one, since it gives you the opportunity to access a new area the which one haven't been finish yet, so... for this update, you can simply forget about that second chest, and only go for the "Fragile key" one.)
Hope it's helpful.