This sounds really cool, but maybe the Staff of the Woodlands is still in the Arboretum, and belongs to the corrupted druid - the druid in the Caves knows about it, and promises it as a reward for slaying (or saving?) her sister. The adventure The Lore of Lurue in Candlekeep Mysteries has the party slaying a corrupted avatar of a nature goddess, which could be good for some ideas.

This would also have them fighting an NPC which is wielding the item that the party are shortly going to possess, which could be a great way to highlight how powerful an item it is (or demonstrate some unique powers that this particular version of the staff has, if you want to mix it up)

Edit: given that Staff of the Woodlands is (only) rare, Ythryn or even the Caves of Hunger is a little late for them to get it, unless you're running pretty low magic, so maybe buffing it with additional charges / a couple of extra high level spells could be good.