I have a huge red FX model stuck on my face when I loaded my custom level, what's that all about?

This is caused by your zone_source csv file to be out of date. The game is trying to load an asset but it can't because the asset it's looking for was not in the zone_source\[levelname].csv file, therefore not getting compiled into the fast file. See the "Update Zone File" category on the Compile Tools page for more information on how to update your zone file with new assets. It's likely that anytime you place a new character into the game you'll need to update the zone_source.