Vlookup with remaining items populated below

Hey guys and gals, I could use some help on the following. I have a list of Feature IDs on a second tab (IDs). The feature IDs link up to the Condition IDs on the Master File tab. I need Column A (Feature IDs) to be populated by doing a lookup of the Condition ID. Then, any feature IDs from the second tab that weren't included in the Master File Column A (Feature IDs) need to populate below the rest of the recently looked up numbers.

The reason I can't just populate all of the Feature IDs is because there will be instances where there are 10 different condition ids to 1 feature id. If there isn't a condition id for the feature id on the second tab, I still need to populate it on the master file tab because it has a special condition id that must be manually entered.

I've attached an excel with the template I'm using.

Thanks so much,
Excelnoob927

Excelforumloookup.xlsx

Would you manually add the expected results to column A so that we can better understand what you mean.